Remove common directory switcher
Remove common directory switcher

Since we finished common directory migration from common-rst
to common, this patch removes common directory switcher, that
is merged at the change I7ba517136807513f982e66010906b97621f844fc,
to migrate common directory for rst files from common-rst to common.

Change-Id: I40aac8ec2d497d83b41048b2576a3a0ab04c8a93

openstack/openstack-doc-tools,openstack/openstack-doc-tools