RFR(s): 8161539: 8159666 breaks minimal VM

[Calvin Cheung]

Summary of change:
- removes the dummy jvmti function bodies in instanceKlass.hpp;
- put "#if INCLUDE_JVMTI" guards at the call sites of those functions.

bug: https://bugs.openjdk.java.net/browse/JDK-8161539
webrev: http://cr.openjdk.java.net/~ccheung/8161539/webrev.00/

It passed JPRT and "tier-2" testing.
It also passed minimal vm build.

thanks,
Calvin