Remove _load_return_value from RPC internal.py

[mrshenli]

Stack from ghstack:

• Don't run user function until all UserRRefs in the args are confirmed #34497 Don't run user function until all UserRRefs in the args are confirmed
• Split deserialize from runPythonUdf and remove generatePythonUDFResult #34496 Split deserialize from runPythonUdf and remove generatePythonUDFResult
• Use SerializedPyObj in PythonRpcHandler::generatePythonUDFResult #34495 Use SerializedPyObj in PythonRpcHandler::generatePythonUDFResult
• Split deserialize from _run_function in RPC internal.py #34494 Split deserialize from _run_function in RPC internal.py
• Use SerializedPyObj in PythonRpcHandler #34493 Use SerializedPyObj in PythonRpcHandler
• Remove _load_return_value from RPC internal.py #34492 Remove _load_return_value from RPC internal.py
• Consolidate Python Messages to use SerializedPyObj #34491 Consolidate Python Messages to use SerializedPyObj
• Avoid copy contents in SerializedPyObj #34490 Avoid copy contents in SerializedPyObj

Differential Revision: D20347468

[dr-ci]

💊 CircleCI build failures summary and remediations

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@mrshenli merged this pull request in 18ef09f.