xfs: use xfs_bmap_del_extent_delay for the data fork as well

And remove the delalloc code from xfs_bmap_del_extent, which gets renamed
to xfs_bmap_del_extent_real to fit the naming scheme used by the other
xfs_bmap_{add,del}_extent_* routines.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>