btrfs: remove unused parameter from readahead_tree_block

The parent_transid parameter has been unused since its introduction in
ca7a79ad8dbe2466 ("Pass down the expected generation number when reading
tree blocks").  In reada_tree_block, it was even wrongly set to leafsize.
Transid check is done in the proper read and readahead ignores errors.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 2d221c4..16cb2b4 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2861,13 +2861,8 @@
 			    struct tree_block *block)
 {
 	BUG_ON(block->key_ready);
-	if (block->key.type == BTRFS_METADATA_ITEM_KEY)
-		readahead_tree_block(rc->extent_root, block->bytenr,
-				     block->key.objectid,
-				     rc->extent_root->nodesize);
-	else
-		readahead_tree_block(rc->extent_root, block->bytenr,
-				     block->key.objectid, block->key.offset);
+	readahead_tree_block(rc->extent_root, block->bytenr,
+			block->key.objectid);
 	return 0;
 }