Remove any category assignments. They look like <nowiki>[[category:some category]]<nowiki>. Links to categories, which do not assign a page to a category, can stay. Category link tags look like <nowiki>[[:category: some category]]</nowiki>.
Also remove any old code that is no longer needed. Exampls Examples include:
<nowiki>
<includeonly>...</includeonly>
flush <!---!-flush -- >
</nowiki>