Remove obsolete netlink_firewall_socket and netlink_ip6fw_socket classes.

The implementation for NETLINK_FIREWALL and NETLINK_IP6_FW protocols
was removed from the kernel in commit
d16cf20e2f2f13411eece7f7fb72c17d141c4a84 ("netfilter: remove ip_queue
support") circa Linux 3.5.  Unless we need to retain compatibility
for kernels < 3.5, we can drop these classes from the policy altogether.

Possibly the neverallow rule in app.te should be augmented to include
the newer netlink security classes, similar to webview_zygote, but
that can be a separate change.

Test: policy builds

Change-Id: Iab9389eb59c96772e5fa87c71d0afc86fe99bb6b
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>