cleanup torch unittests (#6196)

* improve unit tests

this is a sample of one test according to the request in https://github.com/huggingface/transformers/issues/5973
before I apply it to the rest

* batch 1

* batch 2

* batch 3

* batch 4

* batch 5

* style

* non-tf template

* last deletion of check_loss_output

tests/test_modeling_t5.py

@@ -95,9 +95,6 @@ class T5ModelTester:
             lm_labels,
         )
 
-    def check_loss_output(self, result):
-        self.parent.assertListEqual(list(result["loss"].size()), [])
-
     def check_prepare_lm_labels_via_shift_left(
         self, config, input_ids, decoder_input_ids, attention_mask, decoder_attention_mask, lm_labels,
     ):