SELinux: drop useless (and incorrect) AVTAB_MAX_SIZE

AVTAB_MAX_SIZE was a define which was supposed to be used in userspace to
define a maximally sized avtab when userspace wasn't sure how big of a table
it needed.  It doesn't make sense in the kernel since we always know our table
sizes.  The only place it is used we have a more appropiately named define
called AVTAB_MAX_HASH_BUCKETS, use that instead.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>