Delete DVR namespaces on node after removing last VM

Delete DVR namespaces on node after removing last VM

After removing the last VM using a distributed router,
the router's namespaces are still present on the VM host
The problem is that the neutron API server sent the router
remove notification to the L3 agent using the name of the
host running the L3 agent instead of the agent's uuid. This
caused an error when sending the notification. So the L3
agent never had the chance to cleanup the namespace.
This problem is fixed here.

Afterwards, it was found that the notification was still not
sent. The reason is that the router/L3-agent binding has
already been deleted before the routine that sends the
router removed notification was called. The notifier routine
errored out when it tried to delete the same router/L3 agent
binding. This problem is fixed in this patch by removing the
binding removal step from the DVR scheduler.

Change-Id: I6323d7ff438bb6c31e4a794bd3da96bf132fdc85
Closes-Bug: 1353165