btrfs: Clean up unused variables in free-space-tree.c

Remove variables 'start' and 'end', which are set but never used.
Signed-off-by: NChristos Gkekas <chris.gekas@gmail.com>
Reviewed-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/free-space-tree.c

@@ -1286,12 +1286,8 @@ static int __add_block_group_free_space(struct btrfs_trans_handle *trans,
 					struct btrfs_block_group_cache *block_group,
 					struct btrfs_path *path)
 {
-	u64 start, end;
 	int ret;
 
-	start = block_group->key.objectid;
-	end = block_group->key.objectid + block_group->key.offset;
-
 	block_group->needs_free_space = 0;
 
 	ret = add_new_free_space_info(trans, fs_info, block_group, path);