Possible resources leak in void ProcessGroupNCCL::shutdown()

While reviewing the NCCL symmetric-memory cleanup path, I noticed a possible cleanup and lifetime issue in ProcessGroupNCCL::shutdown(). This is currently a code-review question; ProcessGroupNCCL::shutdown() may destroy the communicator with symmetric-memory segement registeration and their cached handles(ncclCommMemPoolMap and registeredSegmentHandles_) are still alive. The following code in shutdown() is for none-symmetric memory pool: // Deregister memory pool after finalizing all collecti...