redis: remove useless dep on msgpack-python
redis: remove useless dep on msgpack-python

This seems to be a left-over since Redis has no particular usage of msgpack.

Change-Id: I7046392ec77650b740c2a89f0069a3bf1f586558

gnocchixyz/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,leandroreox/gnocchi