set AA_EnableHighDpiScaling attribute early

This avoids Qt 5.12.4 and newer spewing a warning:

Attribute Qt::AA_EnableHighDpiScaling must be set before QCoreApplication is created.

src/sakia/app.py

@@ -114,7 +114,6 @@ class Application(QObject):
 
     @classmethod
     def startup(cls, argv, qapp, loop):
-        qapp.setAttribute(Qt.AA_EnableHighDpiScaling, True)
         options = SakiaOptions.from_arguments(argv)
         app_data = AppDataFile.in_config_path(options.config_path).load_or_init()
         app = cls(