build system cleanups

- load(qt_module) => load(qt_build_config)
- remove:
  - setup of PKGCONFIG* variables (automated now)
  - %mastercontent assignment (automated now)
  - pointless QPRO_PWD assignments
  - pointless and commented out include and depend paths
  - qmake -project boilerplate

Change-Id: Ie75ffb4f3ff789a8bfa9f1ddbd92e13c9c9fafa7
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>