ENGINES: We have resetGraphicsScale(), lets use it

If highres games pass defaultTo1XScaler=true to initGraphics(),
use resetGraphicsScale() instead of hardcoding "1x" (which doesn't
exist on the OpenGL backend)
If an OpenGL mode is selected, it now doesn't switch back to plain
SDL now for those games.

engines/engine.cpp

@@ -155,10 +155,7 @@ void initCommonGFX(bool defaultTo1XScaler) {
 
 	// See if the game should default to 1x scaler
 	if (useDefaultGraphicsMode && defaultTo1XScaler) {
-		// FIXME: As a hack, we use "1x" here. Would be nicer to use
-		// getDefaultGraphicsMode() instead, but right now, we do not specify
-		// whether that is a 1x scaler or not...
-		g_system->setGraphicsMode("1x");
+		g_system->resetGraphicsScale();
 	} else {
 		// Override global scaler with any game-specific define
 		if (ConfMan.hasKey("gfx_mode")) {