xfs: add helper to conditionally remove items from the AIL

Several areas of code duplicate a pattern where we take the AIL lock,
check whether an item is in the AIL and remove it if so. Create a new
helper for this pattern and use it where appropriate.

Signed-off-by: Brian Foster <bfoster@redhat.com>

diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 092d652..919057e 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -647,11 +647,7 @@
 			xfs_buf_item_relse(bp);
 		else if (aborted) {
 			ASSERT(XFS_FORCED_SHUTDOWN(lip->li_mountp));
-			if (lip->li_flags & XFS_LI_IN_AIL) {
-				spin_lock(&lip->li_ailp->xa_lock);
-				xfs_trans_ail_delete(lip->li_ailp, lip,
-						     SHUTDOWN_LOG_IO_ERROR);
-			}
+			xfs_trans_ail_remove(lip, SHUTDOWN_LOG_IO_ERROR);
 			xfs_buf_item_relse(bp);
 		}
 	}