Clear LinkCache when failing to fetch Flow board
WorkflowLoaderFactory tries to fetch the workflow id
from page content. For that, it’ll go through
WikiPage::loadPageData, where it won’t be fetched from
master, but (in WikiPage::loadFromRow) be added to
LinkCache. This is likely causing invalid results
because we *just* moved that page in this same request.
The LinkCache stuff in OptInController.php was useless:
resetArticleID already clears link cache as well.
Moved a bit of code in onTitleMove: we shouldn’t be
potentially changing $oldTitle (by fetching article id)
if it’s not Flow-related.