Btrfs: remove some WARN_ONs in the IO failure path

These debugging WARN_ONs make too much console noise during regular
IO failures.  An IO failure will still generate a number of messages
as we verify checksums etc, but these two are not needed.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/disk-io.c

@@ -848,8 +848,6 @@ struct extent_buffer *read_tree_block(struct btrfs_root *root, u64 bytenr,
 
 	if (ret == 0)
 		set_bit(EXTENT_BUFFER_UPTODATE, &buf->bflags);
-	else
-		WARN_ON(1);
 	return buf;
 
 }

fs/btrfs/inode.c

@@ -4296,7 +4296,6 @@ out:
 	}
 	if (err) {
 		free_extent_map(em);
-		WARN_ON(1);
 		return ERR_PTR(err);
 	}
 	return em;