RFR(s): 8235912: JvmtiBreakpoint remove oops_do and metadata_do

[Robbin Ehn]

Hi all, please review.

 From issue, https://bugs.openjdk.java.net/browse/JDK-8235912:

JvmtiBreakpoints are walked via VMThread oops_do (the breakpoint is in a vm 
operation) before they are installed in the safeopint and after they have been 
installed, walked with JvmtiCurrentBreakpoints::oops_do().
By putting the class holder inside oopStorage there is no need for this.

JvmtiCurrentBreakpoints::metadata_do is not needed because redefine classes 
actually removes the breakpoints before updating them (so there is no 
breakpoints to update).
We can just remove metadata_do.


I also removed some unused code.

Changeset:
http://cr.openjdk.java.net/~rehn/8235912/v1/webrev/

Passes several runs of nsk jvmti/jdi and t1-7.

Thanks, Robbin