Cleanup the usage of `layer_norm_eps` in some models
# What does this PR do?

**(No breaking change in this PR)**
**(So far I only change `OneFormerConfig`, but I will update other config classes whose default `layer_norm_eps = 1e-5`)**

Fix the missing usage of `config.layer_norm_eps` in some pytorch models: **if the default value in the config class is `1e-05`** (i.e. the same as the default value in `nn.LayerNorm`. In this case, we don't break the current behavior, and **make the (WIP) test dealing with much fewer edge cases** (which is always a bit of burden).

**In #20699, my claim regarding the breaking change was a bit misleading**: only those config classes having default `layer_norm_eps` not being `1e-5` (for example, `LxmertConfig`) will have breaking change - which I don't do anything in this PR.
_The documentation is not available anymore as the PR was closed or merged._<|||||>@sgugger @NielsRogge  Just want to hear from you to make sure we are good for this change 🙏 before I continue.

I can definitely just add these config classes to a list of edge cases in my (WIP) tests. But I feel it's better to clean them up, so future models won't copy/paste the same code, and we accumulate more and more edge cases to skip in the tests.