Make use of TagEngine::getSubselectForObjectsByTags() in TaggedArticleList

Make use of TagEngine::getSubselectForObjectsByTags() in TaggedArticleList

Commit c9613f130106f74853fbe9a50f06c00208106b8c is fun.

It renamed the getSqlForObjectsByTags() method that was previously used in
TaggedArticleList to the current name getSubselectForObjectsByTags() and fixed
a bug in the method that prevented it from working correctly.

At the same time the commit edited TaggedArticleList to no longer use this
method and instead copied over the logic.

I'm not sure what exactly happened during the development of that commit, but
we simply should use this (fixed) method.