Remove explicit private.

Remove unnecessary delegate.
Use extension method syntax.
Fix HealthInfo.NotifyAppliedDamage’s desc.
Remove unused using directives.
Remove explicit type declaration in Manifest.

OpenRA.Game/ObjectCreator.cs

@@ -10,7 +10,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.IO;
 using System.Linq;
 using System.Reflection;
 using OpenRA.Primitives;