The monolithic package was not used except as a base for qt-4. Disband
this relation and make qt-4 a complete independent package definition.
Thus the monolithic package qt5 and be removed resp. deprecated.
* gnu/packages/qt.scm (qt-4): Copy all relevant package definition
parts from 'qt' and not longer inherit from 'qt'.
(qt): Define as a deprecated alias for 'qtbase`.