Remove directory creation side effect from Platform.SupportDir.

OpenRA.Game/ExternalMods.cs

@@ -123,9 +123,6 @@ namespace OpenRA
 
 			foreach (var source in sources.Distinct())
 			{
-				if (!Directory.Exists(source))
-					continue;
-
 				var metadataPath = Path.Combine(source, "ModMetadata");
 
 				try

OpenRA.Game/Platform.cs

@@ -93,9 +93,6 @@ namespace OpenRA
 					break;
 			}
 
-			if (!Directory.Exists(dir))
-				Directory.CreateDirectory(dir);
-
 			return dir + Path.DirectorySeparatorChar;
 		}