selinux: drop unused socket security classes

selinux: drop unused socket security classes

Several of the extended socket classes introduced by
commit a9cb0dd6d4ce3d29 ("selinux: support distinctions
among all network address families") 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>
Signed-off-by: Paul Moore <paul@paul-moore.com>