Drop MANIFEST.in - it's not needed by pbr

networking-arista already uses PBR:-
setuptools.setup(
	setup_requires=['pbr>=1.8'],
	pbr=True)
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: I4507cac0d45c3ccb46050d31bce6056b783fc4b4

MANIFEST.in

@@ -1,6 +0,0 @@
-include AUTHORS
-include ChangeLog
-exclude .gitignore
-exclude .gitreview
-
-global-exclude *.pyc