[XFS] Kill attr_capable checks as already done in xattr_permission.

No need for addition permission checks in the xattr handler,
fs/xattr.c:xattr_permission() already does them, and in fact slightly more
strict then what was in the attr_capable handlers.

SGI-PV: 981809
SGI-Modid: xfs-linux-melb:xfs-kern:31164a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>