Revert "Fix socket descriptor leak"

Several commands take much longer to complete after that commit.
Therefore, we should revert that specific commit first, and
investigate root cause before merging it back.

This reverts commit 873214b6e2.

Closes-Bug: #1540646
Change-Id: I0eb12f76e93fb1675c78bf60367db534061aceb1

magnum/api/hooks.py

@@ -81,9 +81,6 @@ class RPCHook(hooks.PecanHook):
     def before(self, state):
         state.request.rpcapi = conductor_api.API(context=state.request.context)
 
-    def after(self, state):
-        state.request.rpcapi = None
-
 
 class NoExceptionTracebackHook(hooks.PecanHook):
     """Workaround rpc.common: deserialize_remote_exception.

magnum/common/rpc_service.py

@@ -106,9 +106,6 @@ class API(object):
                                            serializer=serializer,
                                            timeout=timeout)
 
-    def __del__(self):
-        self._client.transport.cleanup()
-
     def _call(self, method, *args, **kwargs):
         return self._client.call(self._context, method, *args, **kwargs)