Get rid of $wgFlowOccupyPages
We already didn’t need this anymore: every board is guaranteed to have an
associated record in page already. We retroactively created missing pages
a while ago with maintenance/FlowUpdateWorkflowPageId.php
(I67ac1bc3def5cce143b7b08b5d4301fe741df09b). At that same time, we also
deployed changes to guarantee a new workflow could not be created without
an associated entry in page.
Since page/revision entries exist, we can read the content model from there
and no longer need $wgFlowOccupyPages.
Theoretically, there could be pages in $wgFlowOccupyPages where a topic was
never created. After this patch, such empty pages would then no longer be
recognized as Flow board. I think it's unlikely there are any such pages
- they were activated on request, so likely to be used
- we’ve been activating them using Special:EnableFlow for a while now, which creates a page entry
Meanwhile also completely removed a bit of code in DeletedContributionsQuery
hook, where we were trying to short-circuit when viewing a namespace that was
guaranteed not to have a Flow page, but that code was already not reliable
since $wgFlowOccupy* aren't the only means of enabling Flow anymore.