Drop the creator_id and updater_id fields from wiki pages. These fields
had several issues:
* The creator_id field was inconsistent with the wiki_page_versions
table. Apparently during the migration to Danbooru 2 in 2012-2013 the
creator_id field got reset to whoever last updated the wiki at that
point in time.
* Saving a wiki would set the updater_id even when nothing actually
changed. This also caused the updated_at timestamp to get bumped.
Because of this, anything that saved a wiki, including things like
creating aliases or implications, would bump the updater_id and
updated_at even though the wiki didn't actually change. This meant
these fields weren't consistent with the wiki_page_versions history.
Changes:
* Remove `creator_name` field from the /wiki_pages.json API.
* Remove creator name search option from /wiki_pages/search.
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