The purgeRedundantText method in the Maintenance.php class removes records from the text table, but it doesn't take into account External Storage (where the actual text is stored in an external table, and the text table only contains a pointer to the real location).

I'm not sure if it is supposed to take External Storage into account or not, but if the idea is to reduce the size of the database, not taking External Storage into account makes this method useless in a wiki with External Storage enabled.