Relinking code would weirdly enough allow clearing of extra/fake user
status on IDs used by affected ID, which would be utterly wrong.
Fairly unclear why this was working OK in reported case before rBa71a513def20,
could not spot any obvious reason just from reading code...
Also, in `libblock_remap_data_update_tags`, only transfer fake user
status if `new_id` is not NULL (otherwise that would have removed that
falg from `old_id`, without actually transferring it to anything).
5188c14718