Remove 'Plans' from left nav

In Juno, 'Plans' has no visible page; it has views for creation
and (later) update.  Separating plan views from general overcloud
deployment views still seems correct now and for future
considerations, but there is no need to have it on the left nav
right now.

Change-Id: If28e292f93183340593b6dc81aa550cce13442ad
Merge "Remove 'Plans' from left nav"