xfs: don't bother calling xfs_rmap_finish_one_cleanup in xfs_rmap_finish_one

In xfs_rmap_finish_one we known the cursor is non-zero when calling
xfs_rmap_finish_one_cleanup and we pass a 0 error variable.  This means
xfs_rmap_finish_one_cleanup is just doing a xfs_btree_del_cursor.

Open code that and move xfs_rmap_finish_one_cleanup to
fs/xfs/xfs_rmap_item.c.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: minor porting changes]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>