* Remove reactions to a user when deleting the user
Fixes#15245
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I have no idea why `create(:vomit_reaction, reactable: user)` gave a
validation error about category being invalid, but `build().save`
worked fine.
* Move relation details to reaction scope `for_user`
Add a user method to access this by passing self to reaction scope
* Create a moderator when flagging user in factory
This might be a missing requirement in the reactions factory - but
this suppresses an error about invalid category I was getting when
setting a privileged reaction on the user via
create(:vomit_reaction, reactable: user)
Everywhere else it looks like we do this with `user: moderator` (where
there's a trusted user in the surrounding context).
* Move trusted user requirement into vomit_reaction factory
* Add a data update script to remove reactions to deleted users
This cleans up the remaining invalid references and should make the
change in #15249 obsolete (i.e. we don't need to limit the view to
exclude items that no longer exist).
421dad2900