Fast transformers import part 1 (#9441)

* Don't import libs to check they are available

* Don't import integrations at init

* Add importlib_metdata to deps

* Remove old vars references

* Avoid syntax error

* Adapt testing utils

* Try to appease torchhub

* Add dependency

* Remove more private variables

* Fix typo

* Another typo

* Refine the tf availability test

src/transformers/dependency_versions_table.py

@@ -12,6 +12,7 @@ deps = {
     "flake8": "flake8>=3.8.3",
     "flax": "flax>=0.2.2",
     "fugashi": "fugashi>=1.0",
+    "importlib_metadata": "importlib_metadata",
     "ipadic": "ipadic>=1.0.0,<2.0",
     "isort": "isort>=5.5.4",
     "jax": "jax>=0.2.0",