[XFS] Remove CONFIG_XFS_SECURITY.

There is no point to the CONFIG_XFS_SECURITY option; it disables the
ability to set security attributes at runtime, but it does not actually
slim down or remove any code for runtime. Just remove it and always allow
security attributes to be set.

SGI-PV: 980310
SGI-Modid: xfs-linux-melb:xfs-kern:30877a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>