[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_audio_classification.py

@@ -28,7 +28,6 @@ from transformers.testing_utils import (
     compare_pipeline_output_to_hub_spec,
     is_pipeline_test,
     nested_simplify,
-    require_tf,
     require_torch,
     require_torchaudio,
     slow,
@@ -193,11 +192,6 @@ class AudioClassificationPipelineTests(unittest.TestCase):
             ],
         )
 
-    @require_tf
-    @unittest.skip(reason="Audio classification is not implemented for TF")
-    def test_small_model_tf(self):
-        pass
-
     @require_torch
     @slow
     def test_top_k_none_returns_all_labels(self):