RFR: 8062206: Remove unusable G1RSLogCheckCardTable command line argument

[Kim Barrett]

Please review this removal of conditional code that appears to have never
worked and doesn't have an apparent repair.

Webrev:
http://cr.openjdk.java.net/~kbarrett/8062206/webrev/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8062206

Testing:
jtreg hotspot/test/[closed/]{gc,runtime}, locally (linux x86_64)
refworkload using G1, locally (linux x86_64)
jprt -testset hotspot

I'll also need a sponsor for this.

Removed from G1RemSet::updateRS() the assertion that all cards are clean after
remembered set updating.  This "invariant" hasn't held during the entire life
of G1 in the hotspot repository.  Presently, cards for young generation are
colored "young_card".  And there are a variety of reasons why cards colored
"dirty_card" may remain so (see G1RemSet::refine_card()), so changing the
assertion to test for no such cards doesn't work either.

Removed the G1RSLogCheckCardTable develop option that controlled the bogus
assertion, since that's all that option does.

Removed CountNonCleanMemRegionClosure class, since it is no longer used.