bcachefs: Don't unlink iters on unsuccessful commit

Where unlink_on_commit is used, on unsuccessfull commit we're likely
retrying the whole update and were going to be using the same iterators
again.

The management of multiple iterators needs to be gone over a fair bit
more at some point...
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_update_leaf.c

@@ -923,8 +923,6 @@ int bch2_trans_commit(struct btree_trans *trans,
 		bch2_trans_unlink_iters(trans, ~trans->iters_touched|
 					trans->iters_unlink_on_commit);
 		trans->iters_touched = 0;
-	} else {
-		bch2_trans_unlink_iters(trans, trans->iters_unlink_on_commit);
 	}
 	trans->nr_updates	= 0;
 	trans->mem_top		= 0;