Removes MANIFEST.in as it is not needed explicitely by PBR
Removes MANIFEST.in as it is not needed explicitely by PBR

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: I6b2852b1683a5cf466b2bb1fd1c97aa033c3f3b2

openstack/oslo.middleware