Generalize problem_type to all sequence classification models (#14180)

* Generalize problem_type to all classification models

* Missing import

* Deberta BC and fix tests

* Fix template

* Missing imports

* Revert change to reformer test

* Fix style

tests/test_modeling_big_bird.py

@@ -435,7 +435,6 @@ class BigBirdModelTest(ModelTesterMixin, unittest.TestCase):
     # head masking & pruning is currently not supported for big bird
     test_head_masking = False
     test_pruning = False
-    test_sequence_classification_problem_types = True
 
     # torchscript should be possible, but takes prohibitively long to test.
     # Also torchscript is not an important feature to have in the beginning.