Kill model archive maps
Links to model weights inside the code are not useful anymore, on the contrary, defining those shortcuts to URLs in code tend to lead to discrepancies with the canonical naming scheme of models at huggingface.co

As an example, we cannot cleanly load [`facebook/bart-large-cnn`](https://huggingface.co/facebook/bart-large-cnn) from either huggingface.co or the inference API because it's aliased to bart-large-cnn in the code.

If this PR is approved, before merging I will:
- do the same thing for configs (easy)
- just rename the renamed model identifiers for tokenizers. (completely getting rid of "archive maps" for tokenizers is way harder because of the hardcoded maps like `PRETRAINED_POSITIONAL_EMBEDDINGS_SIZES` and `PRETRAINED_INIT_CONFIGURATION`)

---

⚠️  **Note that the change in this PR is breaking for the names of the following models:**

```
"cl-tohoku/bert-base-japanese"
"cl-tohoku/bert-base-japanese-whole-word-masking"
"cl-tohoku/bert-base-japanese-char"
"cl-tohoku/bert-base-japanese-char-whole-word-masking"
"TurkuNLP/bert-base-finnish-cased-v1"
"TurkuNLP/bert-base-finnish-uncased-v1"
"wietsedv/bert-base-dutch-cased"
"flaubert/flaubert_small_cased"
"flaubert/flaubert_base_uncased"
"flaubert/flaubert_base_cased"
"flaubert/flaubert_large_cased"

all variants of "facebook/bart"
```

^^ You'll need to specify the organization prefix for those models from now on. However, no files were moved on S3 so this doesn't change anything for all current versions of the library.

However it's a breaking change so we'll be sure to pinpoint to it in the next release.
Love this! is there a plan to allow aliases moving forward?
typing `'Helsinki-NLP/opus-mt-romance-en'` is not awful so I don't feel very strongly that we should, but interested in your thoughts.<|||||>Hmm no I don't see an obvious need for aliases personally.<|||||>Awesome!<|||||># [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=h1) Report
> Merging [#4636](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/88762a2f8cc409fe15a9e6a049fe69ae3197fc49&el=desc) will **decrease** coverage by `0.08%`.
> The diff coverage is `100.00%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4636/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4636      +/-   ##
==========================================
- Coverage   77.12%   77.04%   -0.09%     
==========================================
  Files         128      128              
  Lines       21071    20977      -94     
==========================================
- Hits        16252    16162      -90     
+ Misses       4819     4815       -4     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/configuration\_albert.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2FsYmVydC5weQ==) | `100.00% <ø> (ø)` | |
| [src/transformers/configuration\_bart.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2JhcnQucHk=) | `93.33% <ø> (-0.15%)` | :arrow_down: |
| [src/transformers/configuration\_bert.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2JlcnQucHk=) | `100.00% <ø> (ø)` | |
| [src/transformers/configuration\_camembert.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2NhbWVtYmVydC5weQ==) | `100.00% <ø> (ø)` | |
| [src/transformers/configuration\_ctrl.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2N0cmwucHk=) | `97.05% <ø> (-0.09%)` | :arrow_down: |
| [src/transformers/configuration\_distilbert.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2Rpc3RpbGJlcnQucHk=) | `100.00% <ø> (ø)` | |
| [src/transformers/configuration\_electra.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2VsZWN0cmEucHk=) | `100.00% <ø> (ø)` | |
| [src/transformers/configuration\_flaubert.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2ZsYXViZXJ0LnB5) | `100.00% <ø> (ø)` | |
| [src/transformers/configuration\_gpt2.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2dwdDIucHk=) | `97.22% <ø> (-0.08%)` | :arrow_down: |
| [src/transformers/configuration\_longformer.py](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2xvbmdmb3JtZXIucHk=) | `100.00% <ø> (ø)` | |
| ... and [56 more](https://codecov.io/gh/huggingface/transformers/pull/4636/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=footer). Last update [88762a2...a5f6993](https://codecov.io/gh/huggingface/transformers/pull/4636?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>For configs, I decided to leave the URLs (even if they're not used) to have quick reference and be able to open them from the code. We can always delete them later though.

Ok, merging this!