Tests: move generate tests to the right mixin and delete redundant tests (#34464)

* tmp commit

* tmp commit

* cull overwrites of deleted tests

* typo

* more specific docstring

* make fixup

* parameterize at the top?

* correction

* more deletions :D

* tmp commit

* for VLMs too

* fix _check_outputs

* test nit

* make fixup

* fix another flaky

* test_generate_from_inputs_embeds -- handle missing attention mask

tests/models/idefics/test_modeling_idefics.py

@@ -770,13 +770,6 @@ class IdeficsForVisionText2TextTest(IdeficsModelTest, GenerationTesterMixin, uni
     def test_custom_4d_attention_mask(self):
         pass
 
-    @unittest.skip(
-        reason="IDEFICS has specific requirements for working with inputs embeds like passing also the ids and pixels"
-    )
-    @parameterized.expand([(1,), (2,)])
-    def test_generate_from_inputs_embeds_decoder_only(self, num_beams):
-        pass
-
     @unittest.skip(reason="IDEFICS cannot compile due to dynamic control flow when checking inputs")
     def test_generate_compile_fullgraph(self):
         pass