[Nestmates] RFR: 8195828: [Nestmates] Remove leftover changes to invokespecial handling that are not needed

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8195828
webrev: http://cr.openjdk.java.net/~dholmes/8195828/webrev/

Simple cleanup of changes not needed since we dropped use of 
invokespecial for nestmate support. This minimises differences with 
mainline version.

Thanks,
David