RFR (S) 8198717: Remove compute_optional_offset

[coleen.phillimore at oracle.com]

Summary: remove optional_offset computation and related unused code from 
javaClasses for reflection.

open webrev at http://cr.openjdk.java.net/~coleenp/8198717.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8198717

Tested with hs-tier1 and 2.

Thanks,
Coleen