Revert "shrink_group implementation to expose ncclCommShrink API (#164518)"

This reverts commit fa0db212e717b6cb225159cb32ea3d83baa52381.

Reverted https://github.com/pytorch/pytorch/pull/164518 on behalf of https://github.com/pytorch-auto-revert due to Reverted automatically by pytorch's autorevert, to avoid this behaviour add the tag autorevert: disable ([comment](https://github.com/pytorch/pytorch/pull/164518#issuecomment-3419893217))

torch/testing/_internal/common_distributed.py

@@ -238,47 +238,6 @@ def skip_if_lt_x_gpu(x):
     return decorator
 
 
-def requires_world_size(n: int):
-    """
-    Decorator to request a specific world size for a test. The test harness can
-    read this attribute to set the number of ranks to spawn. If there are fewer
-    than `n` CUDA devices available, the test should be skipped by the harness.
-
-    Usage:
-        @require_world_size(3)
-        def test_something(self):
-            ...
-    """
-
-    def decorator(func):
-        func._required_world_size = n
-        available = torch.cuda.device_count()
-        return unittest.skipUnless(
-            available >= n, f"requires {n} GPUs, found {available}"
-        )(func)
-
-    return decorator
-
-
-def get_required_world_size(obj: Any, default: int) -> int:
-    """
-    Returns the requested world size for the currently running unittest method on `obj`
-    if annotated via `@require_world_size(n)`, else returns `default`.
-    """
-    try:
-        # Try MultiProcessTestCase helper first, then unittest fallback
-        test_name = (
-            obj._current_test_name()  # type: ignore[attr-defined]
-            if hasattr(obj, "_current_test_name") and callable(obj._current_test_name)
-            else obj._testMethodName
-        )
-        fn = getattr(obj, test_name)
-        value = fn._required_world_size
-        return int(value)
-    except Exception:
-        return default
-
-
 # This decorator helps avoiding initializing cuda while testing other backends
 def nccl_skip_if_lt_x_gpu(backend, x):
     def decorator(func):
@@ -408,13 +367,6 @@ def requires_nccl_version(version, msg):
         )
 
 
-def requires_nccl_shrink():
-    """
-    Require NCCL shrink support (NCCL available and version >= 2.27).
-    """
-    return requires_nccl_version((2, 27), "Need NCCL 2.27+ for shrink_group")
-
-
 def requires_nccl():
     return skip_but_pass_in_sandcastle_if(
         not c10d.is_nccl_available(),