A few of the socket classes added by commit 09ebf2b59a ("refpolicy:
Define extended_socket_class policy capability and socket classes") are
never used because sockets can never be created with the associated
address family. Remove these unused socket security classes.
The removed classes are bridge_socket for PF_BRIDGE, ib_socket for PF_IB,
and mpls_socket for PF_MPLS.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>