ovl: Get rid of ovl_xattr_noacl_handlers array

ovl: Get rid of ovl_xattr_noacl_handlers array

Use an ordinary #ifdef to conditionally include the POSIX ACL handlers
in ovl_xattr_handlers, like the other filesystems do.  Flag the code
that is now only used conditionally with __maybe_unused.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Orabug: 26401569

(backport upstream commit 0c97be22f928b85110504c4bbb8574facb4bd0c0)

Signed-off-by: Shan Hai <shan.hai@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>