[tests] remove TF tests (uses of require_tf) (#38944)

* remove uses of require_tf

* remove redundant import guards

* this class has no tests

* nits

* del tf rng comment

tests/pipelines/test_pipelines_document_question_answering.py

@@ -27,7 +27,6 @@ from transformers.testing_utils import (
     nested_simplify,
     require_detectron2,
     require_pytesseract,
-    require_tf,
     require_torch,
     require_torch_bf16,
     require_vision,
@@ -423,8 +422,3 @@ class DocumentQuestionAnsweringPipelineTests(unittest.TestCase):
         question = "What is the invoice number?"
         outputs = dqa_pipeline(image=image, question=question, top_k=2)
         self.assertEqual(nested_simplify(outputs, decimals=4), [{"answer": "us-001"}])
-
-    @require_tf
-    @unittest.skip(reason="Document question answering not implemented in TF")
-    def test_small_model_tf(self):
-        pass