Revert D28617214: [Gradient Compression] Do not skip the comm hook te…

…sts on Gloo backend

Test Plan: revert-hammer

Differential Revision:
D28617214 (3e88acb)

Original commit changeset: 3bafb0c837a1

fbshipit-source-id: 0b6254e9766436633faea63cd64c454b739f74b4

torch/testing/_internal/distributed/distributed_test.py

@@ -3330,8 +3330,8 @@ def test_DistributedDataParallel_non_default_stream(self):
                     )
 
         @unittest.skipIf(
-            BACKEND != "nccl" and BACKEND != "gloo",
-            "MPI backend does not support DDP communication hook on CUDA devices",
+            BACKEND != "nccl",
+            "Only NCCL backend supports DDP communication hook",
         )
         @skip_if_lt_x_gpu(int(os.environ["WORLD_SIZE"]))
         @skip_if_rocm
@@ -3441,17 +3441,17 @@ def _test_ddp_hook_parity(self, state, hook):
                 )
 
         @unittest.skipIf(
-            BACKEND != "nccl" and BACKEND != "gloo",
-            "MPI backend does not support DDP communication hook on CUDA devices",
+            BACKEND != "nccl",
+            "Only NCCL backend supports DDP communication hook",
         )
         @skip_if_lt_x_gpu(int(os.environ["WORLD_SIZE"]))
         @skip_if_rocm
         def test_ddp_hook_parity_allreduce(self):
             self._test_ddp_hook_parity(state=None, hook=default.allreduce_hook)
 
         @unittest.skipIf(
-            BACKEND != "nccl" and BACKEND != "gloo",
-            "MPI backend does not support DDP communication hook on CUDA devices",
+            BACKEND != "nccl",
+            "Only NCCL backend supports DDP communication hook",
         )
         @skip_if_lt_x_gpu(int(os.environ["WORLD_SIZE"]))
         @skip_if_rocm
@@ -3463,8 +3463,8 @@ def test_ddp_hook_parity_allreduce_process_group(self):
             self._test_ddp_hook_parity(state=process_group, hook=default.allreduce_hook)
 
         @unittest.skipIf(
-            BACKEND != "nccl" and BACKEND != "gloo",
-            "MPI backend does not support DDP communication hook on CUDA devices",
+            BACKEND != "nccl",
+            "Only NCCL backend supports DDP communication hook",
         )
         @skip_if_lt_x_gpu(int(os.environ["WORLD_SIZE"]))
         @skip_if_rocm