[XFS] kill xfs_uuid_unmount

Quite useless wrapper that doesn't help making the code more readable.

SGI-PV: 981498
SGI-Modid: xfs-linux-melb:xfs-kern:31184a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>