Remove setuptools-git from setup.py.

Put it in test-requires so it's there when we build a tarball.
Change-Id: I8a5adec74beeb397e71e17030338a8051fe6fb0b
Reviewed-on: https://review.openstack.org/19885
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins