RFR: 8240722: [BACKOUT] G1DirtyCardQueue destructor has useless flush

[Kim Barrett]

Please review this backout of JDK-8240133, which turns out to have
problems and needs a bit of a rethink; see JDK-8240722 for details.

CR:
[backout] https://bugs.openjdk.java.net/browse/JDK-8240722
[original] https://bugs.openjdk.java.net/browse/JDK-8240133

Webrev:
https://cr.openjdk.java.net/~kbarrett/8240722/open.00/

Testing:
Local build.