RFR: 8030646: Track collection set membership in one place

[Erik Helin]

Hi all,

this (rather) small patch removes the field
HeapRegion::_in_collection_set and instead only uses the
G1BiasedMappedArray G1CollectedHeap::_in_cset_fast_test to track
collection set membership. Given that _in_cset_fast_test already track
collection set membership, the _in_collection_set field in HeapRegion is
redundant, it is only messy to keep track of this information in two
places.

Patch:
http://cr.openjdk.java.net/~ehelin/8030646/webrev.00/

Issue:
https://bugs.openjdk.java.net/browse/JDK-8030646

Testing:
- JPRT
- GCBasher (locally, Linux x86-64)
- Ad-hoc:
  - BigApps:
    - DaCapo
    - runThese
    - Kitchensink
    - Weblogic
  - Regression:
    - nashorn
    - hotspot
  - vm:
    - stress
    - compiler
    - gc
    - runtime
    - quick
    - oom
    - parallel class loading
    - regression

Thanks,
Erik