Remove kdocumentviewer
It was causing problems (Windows build fails) now that we enabled -Wweak-vtables (and probably before didn't work that much before, guessing that's why we had that if (doc) in openFile) This is the simplest solution, invokeMethod is not great but we already use it, so it's not too terrible The openDocument function was unused so remove it. The other two solutions are: * Make KDocumentViewer be part of okularcore and then link the okularcore to the okular binary, not nice * Make another dynamic library that just contains the KDocumentViewer class, but i'd rather not add yet another library we have to install and take care of