Remove legacy sound code and simplify platform init.

OpenRA.Game/Settings.cs

@@ -102,8 +102,6 @@ namespace OpenRA
 
 	public class GraphicSettings
 	{
-		public string Renderer = "Default";
-
 		[Desc("This can be set to Windowed, Fullscreen or PseudoFullscreen.")]
 		public WindowMode Mode = WindowMode.PseudoFullscreen;
 
@@ -142,7 +140,6 @@ namespace OpenRA
 		public bool Shuffle = false;
 		public bool Repeat = false;
 
-		public string Engine = "Default";
 		public string Device = null;
 
 		public bool CashTicks = true;
@@ -162,6 +159,8 @@ namespace OpenRA
 		public string Mod = "modchooser";
 		public string PreviousMod = "ra";
 
+		public string Platform = "Default";
+
 		public bool ShowShellmap = true;
 
 		public bool ViewportEdgeScroll = true;