Stop running jobs for stable/havana

The last Havana stable point release, 2013.2.4, has come and gone.
As it is no longer under support by the vulnerability management
team and stable branch maintainers, remove testing for it. Note that
this also means ceasing grenade jobs for stable/icehouse changes,
since they begin by deploying stable/havana.

Change-Id: Idac2f43d19dff78c3b0ff3c155f3835cafac446e
Merge "Stop running jobs for stable/havana"