xfs: remove xfs_reflink_remap_range

Since xfs_file_remap_range is a thin wrapper, move the contents of
xfs_reflink_remap_range into the shell.  This cuts down on the vfs
calls being made from internal xfs code.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>