selinux: remove unused enumeration constant from selinuxfs

Remove the unused enumeration constant, SEL_AVC, from the sel_inos
enumeration in selinuxfs.

Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>
Acked-by: Eric Paris <eparis@parisplace.org>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>