OPENFLOW-1.1+: OFPRR_METER_DELETE is used

My reading of handle_delete_meter() is that OFPRR_METER_DELETE is used.
Accordingly delete the entry relating to it from OPENFLOW-1.1+.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>