RFR: 8228991: Obsolete -XX:UseAdaptiveGCBoundary

[Kim Barrett]

Please review this change which obsoletes the boolean product flag
-XX:UseAdaptiveGCBoundary and removed the supporting code.

As discussed in the associated CSR, this feature has had a long bug
tail and does not appear to have ever really worked, so we're going
straight to obsoleting the option and removing the code, rather than
first deprecating it.

This mostly involves removal of a bunch of code.  In some places there
are functions which previously needed to be virtual but no longer need
that because the derived classes no longer exist.

There is an assertion in ParallelScavengeHeap::initialize() that was
changed by removing !UseAdaptiveGCBoundary from a disjunction, which
is not what one would expect if making that option unconditionally
false.  It looks like the presence of a test for that option never
mattered, as except in the heterogeneous heap case the virtual spaces
have always supposed to meet (it's using AdjoiningGenerations after
all) and did so.
 
CR:
https://bugs.openjdk.java.net/browse/JDK-8228991
https://bugs.openjdk.java.net/browse/JDK-8242164 (CSR)

Webrev:
https://cr.openjdk.java.net/~kbarrett/8228991/open.00/

Testing:
mach5 tier1-5.
Note: Unable to test nvdimm usage since we don't have any machines
with that configuration.