Remove duplicated config doc

Remove the list of config options from configuration.rst and add
reference to the OS Manuals Configuration Reference, which is the proper
place for this information. With this change the duplication of docco
is also removed.

Latest Config Reference update patch:
https://review.openstack.org/#/c/132997/

Closes-Bug: #1380605
Change-Id: I6293d2e92bdb3dcf8fbadf5d33d63cf38342c528
Merge "Remove duplicated config doc"