Don't follow QT_DEVICE_PIXEL_RATIO

Setting this means we get scaled screen geometry from Qt, and everything
becomes confusing when commmunicating with apps that might not have
this set.

As we use plasma units for UI everything is scaled anyway.

REVIEW: 123115

main_wayland.cpp

@@ -372,6 +372,7 @@ KWIN_EXPORT int kdemain(int argc, char * argv[])
     qWarning() << "QtWayland 5.4.2 required, application might freeze if not present!";
 #endif
 
+    qunsetenv("QT_DEVICE_PIXEL_RATIO");
     qputenv("WAYLAND_SOCKET", QByteArray::number(server->createQtConnection()));
     KWin::ApplicationWayland a(argc, argv);
     a.setupTranslator();

main_x11.cpp

@@ -262,6 +262,8 @@ KWIN_EXPORT int kdemain(int argc, char * argv[])
     // enforce xcb plugin, unfortunately command line switch has precedence
     setenv("QT_QPA_PLATFORM", "xcb", true);
 
+    qunsetenv("QT_DEVICE_PIXEL_RATIO");
+
     KWin::ApplicationX11 a(argc, argv);
     a.setupTranslator();