RFR(XS) 8209823 Replace Verifier::load_class with a simple lookup of super classes

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8209823
8209823-simplify-verifier-load-class.v01/

Please review this small clean up:

Verifier::load_class(name) is called only when name is known to
be the name of a super class of the current class. At this point,
the super class should have already been loaded. Also, the loader
of the current class should have already recorded the super
class as a dependency.

Therefore, load_class does a lot of work (such as resolving the
super class by name) that's not necessary. Also, load_class is
declared to potentially throw exceptions. This makes code analysis
more complicated.

The fix is to remove load_class() altogether and change
ClassVerifier::name_in_supers to also return the super's.
InstanceKlass*

Thanks
- Ioi