btrfs: remove stale comment about locking at btrfs_search_slot()

The comment refers to the old extent buffer locking code, where we used to
have custom locks that had blocking and spinning behaviour modes. That is
not the case anymore, since we have transitioned to rw semaphores, so the
comment does not offer any value anymore. Remove it.
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ctree.c

@@ -1964,10 +1964,6 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		}
 cow_done:
 		p->nodes[level] = b;
-		/*
-		 * Leave path with blocking locks to avoid massive
-		 * lock context switch, this is made on purpose.
-		 */
 
 		/*
 		 * we have a lock on b and as long as we aren't changing