remove SharedDDP as it is deprecated (#25702)

* remove SharedDDP as it was drepracated

* apply review suggestion

* make style

* Oops,forgot to remove the compute_loss context manager in Seq2SeqTrainer.

* remove the unnecessary conditional statement

* keep the logic of IPEX

* clean code

* mix precision setup & make fixup

---------

Co-authored-by: statelesshz <jihuazhong1@huawei.com>

src/transformers/testing_utils.py

@@ -42,7 +42,6 @@ from transformers import logging as transformers_logging
 
 from .integrations import (
     is_clearml_available,
-    is_fairscale_available,
     is_optuna_available,
     is_ray_available,
     is_sigopt_available,
@@ -871,13 +870,6 @@ def require_deepspeed(test_case):
     return unittest.skipUnless(is_deepspeed_available(), "test requires deepspeed")(test_case)
 
 
-def require_fairscale(test_case):
-    """
-    Decorator marking a test that requires fairscale
-    """
-    return unittest.skipUnless(is_fairscale_available(), "test requires fairscale")(test_case)
-
-
 def require_apex(test_case):
     """
     Decorator marking a test that requires apex