RFR: 8066827: Remove ReferenceProcessor::clean_up_discovered_references()

[Kim Barrett]

Note: I will need a sponsor for this change.

Please review this change to replace the one call to
ReferenceProcessor::clean_up_discovered_references() with a call to
ReferenceProcessor::abandon_partial_discovery(), and then remove the
clean_up function and some follow-on cleanup.

As noted in the bug report, the benefit from passing a partial
discovery list from the CMS collector to the compacting collector is
questionable, while incurring significant complexity and appearing to
impose a performance cost on the reference processing of other
collectors, e.g. the need for
DiscoveredListIterator::update_discovered(). 

The change to disable and abandon rather than "clean up" the
discovered list allows us to change the call to
ReferenceProcessor::enable_discovery() by
CMSCollector::do_compaction_work() to pass true values for both
arguments, rather than false values as previously needed.  As a result
of this, the first argument (verify_disabled) is no longer needed, as
all callers always pass true.  Also as a result, the only caller
providing a false value for the second argument (verify_no_refs) is
the destructor for NoRefDiscovery.  So I've eliminated the first
argument and made the second default to true, and updated all of the
callers accordingly (all but ~NoRefDiscovery passing no arguments).

The bug report suggests that the calls to
DiscoveredListIterator::update_discovered() are no longer needed and
that function can also be removed.  I'm deferring that (I'll be filing
a new RFE) because that's a more complex change to analyze and test,
so I'm separating it from this much simpler to understand change.

CR:
https://bugs.openjdk.java.net/browse/JDK-8066827 

Webrev:
http://cr.openjdk.java.net/~kbarrett/8066827/webrev/

Testing: JPRT, local jtreg of gc tests
refworkload with CMS as the collector, with TraceCMSState enabled so I
could examine the logs and verify some of the tests passed through the
changed code; there were 113 occurrences with an iteration count of 1.

JPRT was after Bengt's recent changes to include gc jtreg tests.