Remove old, outdated keystone devref docs

The doc/source/old directory contained several docs
that were marked as 'old' and hadn't been updated for more
than a year.

This patch simply removes them - they aren't referred to in
any way noticable on keystone.openstack.org.

Change-Id: Ida57e0321be09aa8ddcb966f386132946017cdcb
Merge "Remove old, outdated keystone devref docs"