engine: Drop PORT_MIRRORING action group

Since the permissions for using port mirroring on
a specific networks are replaced by using a vnic
profile configured for port mirroring, there is no
more use of the PORT_MIRRORING action group and it
should be removed.

Change-Id: I3111db10372deaa4a244b4d253b72326edd56fe8
Signed-off-by: Moti Asayag <masayag@redhat.com>