Remove persistence wiki page link
Remove persistence wiki page link

All of the relevant docs have been moved over to the
developer docs and the only thing left on the wiki
page is a high-level intro and a link to the developer
docs.

Change-Id: I1fcc5d34586bad3d92fa8bb5043c55249e1c9bdd

jimbobhickville/taskflow,pombredanne/taskflow-1,pombredanne/taskflow-1,junneyang/taskflow,junneyang/taskflow,jimbobhickville/taskflow,openstack/taskflow,openstack/taskflow