xfs: remove if_real_bytes

xfs: remove if_real_bytes

Source kernel commit: fcacbc3f511338842dd177e2d53d457f9741543b

The field is only used for asserts, and to track if we really need to do
realloc when growing the inode fork data.  But the krealloc function
already performs this check internally, so there is no need to keep track
of the real allocation size.

This will free space in the inode fork for keeping a sequence counter of
changes to the extent list.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>