Revert "Do not reset default stream for StreamSafeCUDAAllocator (#42149)"

This reverts commit 6553a9d7.

paddle/fluid/memory/allocation/allocator_facade.cc

@@ -415,23 +415,6 @@ class AllocatorFacadePrivate {
   void SetDefaultStream(const platform::CUDAPlace& place, gpuStream_t stream) {
     const std::shared_ptr<StreamSafeCUDAAllocator>& allocator =
         GetDefaultStreamSafeCUDAAllocator(place);
-
-    // NOTE(Ruibiao): The default stream will be set when the CUDADeviceContext
-    // created. Normally, the DeviceContextPool is a global singleton and one
-    // Place only correspond to one DeviceContext. However, to support
-    // multi-stream scheduling, standalone executor creates two extra
-    // DeviceContextPools for H2D and D2H stream in StreamAnalyzer, which make
-    // one Place correspond to multiple DeviceContext and unexpectedly reset the
-    // default stream in runtime. To avoid this behavior, we do not allow
-    // changing default stream after initially setting.
-    if (allocator->GetDefaultStream() != nullptr) {
-      VLOG(5) << "The default stream for StreamSafeCUDAAllocator("
-              << allocator.get() << ") in " << place << " has been set to "
-              << allocator->GetDefaultStream()
-              << " before, not allow to change now.";
-      return;
-    }
-
     allocator->SetDefaultStream(stream);
     VLOG(8) << "Set default stream to " << stream
             << " for StreamSafeCUDAAllocator(" << allocator.get() << ") in "