RFR: 8243146: Further cleanups after UseAdaptiveGCBoundary removal

[Kim Barrett]

> On Apr 20, 2020, at 4:43 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
> 
> Hi all,
> 
> Please review this patch to further cleanup after the UseAdaptiveGCBoundary removal.
> 
> https://cr.openjdk.java.net/~stefank/8243146/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8243146
> 
> Changes in the patch:
> - Remove AdjoiningGenerations and inline the contents into ParallelScavengeHeap::initialize.
> - Remove AdjoiningVirtualSpaces.
> - Remove PSVirtualSpaceHighToLow
> - Update PS{Old,Young}Gen:
> -- Move initialization to constructors, and made the functions private.
> -- Remove unused functions
> -- Change protected to private
> -- Remove most virtual declarations
> - WB_PSVirtualSpaceAlignment - inlined the old value. There seems to be some, arguably, odd usage of GenAlignment where SpaceAlignment seems more appropriate. They both contain the same value, but it looks weird. Maybe something to fix in a separate RFE.
> 
> Thanks,
> StefanK

Looks good.