Use EGL+GLES workaround for Nvidia X11

We can avoid disabling EGL entirely by forcing Qt to use GLES,
which is not impacted by the black window issue. This lets us
simplify back to EGL everywhere.

app/utils.h

@@ -11,6 +11,5 @@ namespace WMUtils {
     bool isRunningWayland();
     bool isRunningWindowManager();
     bool isRunningDesktopEnvironment();
-    bool isX11EGLSafe();
     QString getDrmCardOverride();
 }