Revert low cpu mem tie weights (#29135)

* Revert "Add tie_weights() to LM heads and set bias in set_output_embeddings() (#28948)"

This reverts commit 725f4ad1cc.

* Revert "Patch to skip failing `test_save_load_low_cpu_mem_usage` tests (#29043)"

This reverts commit 4156f517ce.

tests/models/reformer/test_modeling_reformer.py

@@ -687,12 +687,6 @@ class ReformerLocalAttnModelTest(ReformerTesterMixin, GenerationTesterMixin, Mod
     def test_left_padding_compatibility(self):
         pass
 
-    @unittest.skip(
-        "Not currently compatible. Fails with - NotImplementedError: Cannot copy out of meta tensor; no data!"
-    )
-    def test_save_load_low_cpu_mem_usage(self):
-        pass
-
 
 @require_torch
 class ReformerLSHAttnModelTest(
@@ -854,12 +848,6 @@ class ReformerLSHAttnModelTest(
     def test_left_padding_compatibility(self):
         pass
 
-    @unittest.skip(
-        "Not currently compatible. Fails with - NotImplementedError: Cannot copy out of meta tensor; no data!"
-    )
-    def test_save_load_low_cpu_mem_usage(self):
-        pass
-
 
 @require_torch
 @require_sentencepiece