datapath: Remove vport_del_all() because it is now a no-op.

datapath: Remove vport_del_all() because it is now a no-op.

vport_del_all() was created when vports could exist without being attached
to any datapath.  Now, a vport is always attached to a datapath.  This
function was only called on module unload, but the module can't be unloaded
if any datapath exists, so it won't ever have any work to do, and we might
as well delete it entirely.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Suggested-by: Jesse Gross <jesse@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>