xfs: kill ino64 mount option

The ino64 mount option adds a fixed offset to 32bit inode numbers
to bring them into the 64bit range.  There's no need for this kind
of debug tool given that it's easy to produce real 64bit inode numbers
for testing.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Felix Blyakher <felixb@sgi.com>