remove useless step in cleanup_rpc_backend

It shall not make dir of /var/run/openstack for the cleanup operation.

install_rpc_backend will make the directory, which is covered by another
take care of this.

Change-Id: I2bf1bfb4a6b409cc04f2d7b94dd58627e0134b71
Merge "remove useless step in cleanup_rpc_backend"