Drop MANIFEST.in
Drop MANIFEST.in

This patch removes `MANIFEST.in` file as pbr generates
a sensible manifest from git files and some standard
files and it removes the need for an explicit `MANIFEST.in` file.

Change-Id: Ic8021328145f047af9766a1521193a7837b371e3

openstack/python-brick-cinderclient-ext,openstack/python-brick-cinderclient-ext