Revert changes that made effects static plugins

As it turns out, it slows down Qt plugin loading quite a lot.

Initially, metadata didn't include translated strings but as soon as translators started adding strings, kwin started freezing any time it needed to load a QImage.

The root cause of the freeze is that QStaticPlugin::metaData() doesn't cache json metadata. It performs cbor -> json conversion every time it is called. That combined with a lot of translated strings results in noticeable kwin slowdowns.