Fix dev-python/PyQt5 dependencies

I don't use unity, but since this overlay seems to be the only one providing PyQt5, I use it. However, when I've tried installing it, I ran into multiple problems, which I've fixed with these changes:

```
Added missing dev-qt/qtnetwork, dev-qt/linguist-tools and dev-
qt/qtwidgets dependencies to PyQt5.

Also, removed a configure operation which ran qmake in the qpy/ folder.
That operation seems to be inherited from PyQt4 and now obsolete. This
made the configure phase fail because there's no ".pro" file in the qpy/
subfolders.
```

I'm unsure about the second change, but it really seems like it would always fail. Has the PyQt5 ebuild ever worked?