[Backport] Use ubuntu instead of gcc based images

(adapted from commit MeVisLab/pythonqt@a93104d)

- also remove unneeded "pydebug.h" include
  -> fixes commontk#81

Author: mrbean-bremen

src/PythonQt.cpp

@@ -58,7 +58,6 @@
 
 #include <QDir>
 
-#include <pydebug.h>
 #include <vector>
 
 PythonQt* PythonQt::_self = nullptr;