Revert "[2/3] 3D Composability - move pp tests (pytorch#129801)"

This reverts commit 84cd062.

Reverted pytorch#129801 on behalf of https://github.com/atalman due to Broke periodic CI: distributed/_composable/test_composability/test_pp_composability.py::ComposabilityTest::test_manual_with_data_parallel_dp_type_DDP_ScheduleClass4 [GH job link](https://github.com/pytorch/pytorch/actions/runs/10083807511/job/27882848654) [HUD commit link](https://hud.pytorch.org/pytorch/pytorch/commit/544f950d14e8ce4da0e592d9a3faac349e718151) ([comment](pytorch#129801 (comment)))

.ci/pytorch/multigpu-test.sh

@@ -52,9 +52,11 @@ time python test/run_test.py --verbose -i distributed/tensor/parallel/test_tp_ra
 # FSDP2 tests
 time python test/run_test.py --verbose -i distributed/_composable/fsdp/test_fully_shard_training -- -k test_2d_mlp_with_nd_mesh
 
+# Pipelining composability tests
+time python test/run_test.py --verbose -i distributed/pipelining/test_composability.py
+
 # ND composability tests
 time python test/run_test.py --verbose -i distributed/_composable/test_composability/test_2d_composability
-time python test/run_test.py --verbose -i distributed/_composable/test_composability/test_pp_composability
 
 # Other tests
 time python test/run_test.py --verbose -i test_cuda_primary_ctx

test/distributed/_composable/test_composability/test_pp_composability.py → test/distributed/pipelining/test_composability.py

@@ -1,9 +1,12 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates
 # Owner(s): ["oncall: distributed"]
 import copy
 import os
 import sys
 import tempfile
 
+from model_registry import MLPModule
+
 import torch
 import torch.distributed as dist
 import torch.nn as nn
@@ -35,21 +38,6 @@
 )
 
 
-# MLP Layer
-class MLPModule(torch.nn.Module):
-    def __init__(self, d_hid: int):
-        super().__init__()
-        self.net1 = torch.nn.Linear(d_hid, d_hid)
-        self.relu = torch.nn.ReLU()
-        self.net2 = torch.nn.Linear(d_hid, d_hid)
-
-    def forward(self, x):
-        x = self.net1(x)
-        x = self.relu(x)
-        x = self.net2(x)
-        return x
-
-
 class ComposabilityTest(MultiProcContinousTest):
     @classmethod
     def backend_str(cls) -> str: