pbrd: only remove interface after all seq uninstalled

pbrd: only remove interface after all seq uninstalled

Only remove the interface from the pbr_map after we get
a callback from zapi that every sequence using that interface
has been removed.

Before, if we created a map with multiple sequences and put that on an interface,
then removed it from that interface, it would fail to mark the sequences after
the first one as uninstalled.

This was because we failed to lookup the other ones after we removed
the interface from the pbr_map.

This patch adds a conditional to only delete the interface from the pbr
map if all its sequneces using that interface have been uninstalled.

This patch extends the work done in 38e9ccde2f8edd6946d48c80967027d05e64d73f

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>