Remove py.typed
The experiment was fun (not).

As we are getting a rise in issues of users complaining typecheckers are not happy with our annotations, which we have chosen to keep simple for the sake of documentation, this PR removes the `py.typed` file indicating to type-checkers that Transformers is properly typed.

It is not, and it won't be in the near future because static type-checking things in Python requires sacrificing too much in term of clarity of code (at least in my opinion). This PR just makes it "official".
_The documentation is not available anymore as the PR was closed or merged._