Because:
1. It is a mere alias of `pythonPackages.sip`
2. It is usually not needed since propagated by `pyqt4`
3. It makes it easy to have a packages depend on two different versions
of sip
polkit-qt-1 is upgraded to the latest version, which supports Qt 5. The
attributes are also renamed to differentiate the Qt 4 and Qt 5
branches. The prior naming scheme differentiated between polkit-qt-1 and
polkit-qt, but we no longer package the latter.
