Remove unused files

`MANIFEST.in` was used to handle git files but now pbr can do it instead.
`openstack-common.conf` was used to copy files from oslo-incubator, but
oslo-incubator is no longer maintained. So delete the two files from repo.

Change-Id: I976434e8283c588191d7bfb9321f46cea724406a

MANIFEST.in

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

openstack-common.conf

@@ -1,10 +0,0 @@
-[DEFAULT]
-
-# The list of modules to copy from oslo-incubator.git
-module=apiclient
-module=cliutils
-module=_i18n
-
-
-# The base module to hold the copy of openstack.common
-base=watcherclient