Remove low_cpu_mem_usage and _fast_init (#36963)

* Remove low_cpu_mem_usage and _fast_init

* Update deepspeed.py

* Update modeling_utils.py

* remove the first 2 tests everywhere

* Update test_modeling_common.py

* remove what was remaining about fast_init

* fix logic and simplify

* mismatched keys logic update

* Update modeling_utils.py

* Update modeling_utils.py

* Update modeling_utils.py

* Update modeling_utils.py

* fix 2 models init_weights

* extend to others

* remove grad

* Update modeling_fsmt.py

* init weights in tests

* style

* Update test_modeling_fsmt.py

* more old models

* fix more init_weights

* copies

* fix

* style

* Update modeling_lxmert.py

* fix inits

* more and more

* more

* should finalize

* style

* Update modeling_dinov2_with_registers.py

* fix

* Update modeling_encoder_decoder.py

* fix

* style

* Update modeling_lxmert.py

* post rebase cleanup

* Update modeling_informer.py

* back to start for device

* fix

* add test to detect all failing cases correctly

* Update test_modeling_common.py

* fix

* fix

* sam

* style

* Update modeling_maskformer_swin.py

* CIs

* CIs

* remove test - will add it on separate PR

* fix

* fix

* Update modeling_sam.py

* CIs

* CIs

* CIs

* convnext

* suggestions

* CIs

* fix copies after merge

---------

Co-authored-by: Yih-Dar <2521628+ydshieh@users.noreply.github.com>

tests/models/persimmon/test_modeling_persimmon.py

@@ -379,11 +379,6 @@ class PersimmonModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineTester
             (self.model_tester.batch_size, self.model_tester.seq_length, self.model_tester.num_labels),
         )
 
-    @unittest.skip(reason="Persimmon buffers include complex numbers, which breaks this test")
-    # Copied from tests.models.llama.test_modeling_llama.LlamaModelTest.test_save_load_fast_init_from_base
-    def test_save_load_fast_init_from_base(self):
-        pass
-
     @parameterized.expand([("linear",), ("dynamic",)])
     # Copied from tests.models.llama.test_modeling_llama.LlamaModelTest.test_model_rope_scaling_from_config with Llama->Persimmon
     def test_model_rope_scaling_from_config(self, scaling_type):