Removes coremod (#3038)

From now on every integration must not rely on method stripping through
a coremod or @Optional. Notable example for a very good solution is IC2.

As consequence this drops all support for RF and mods must support on of
our supported energy types. At the time of writing, ForgeEnergy and
IC2/EU.

src/main/java/appeng/core/CommonHelper.java

@@ -62,6 +62,4 @@ public abstract class CommonHelper
 
 	public abstract void updateRenderMode( EntityPlayer player );
 
-	public abstract void missingCoreMod();
-
 }