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/server/ServerHelper.java

@@ -162,12 +162,6 @@ public class ServerHelper extends CommonHelper
 		this.renderModeBased = player;
 	}
 
-	@Override
-	public void missingCoreMod()
-	{
-		throw new IllegalStateException( "Unable to Load Core Mod, please verify that AE2 is properly install in the mods folder, with a .jar extension." );
-	}
-
 	protected CableRenderMode renderModeForPlayer( final EntityPlayer player )
 	{
 		if( player != null )