mon: remove laggy standby nodes (instead of marking laggy)
mon: remove laggy standby nodes (instead of marking laggy)

This will implicitly clean out old standby nodes that go away.  Laggy
cmds's that don't will just re-add themselves.  Since the laggy flag is
a map change, this creates no more or less map churn.

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph