btrfs: remove unused qgroup members from btrfs_trans_handle

The members have been effectively unused since "Btrfs: rework qgroup
accounting" (fcebe456), there's no substitute for
assert_qgroups_uptodate so it's removed as well.

Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>