RFR: 8300769: Remove G1CollectionSet::_inc_bytes_used_before [v3]

[Thomas Schatzl]

> Hi all,
> 
>   please review this removal of `G1CollectionSet::_inc_bytes_used_before`; this variable holds the amount of bytes used in eden regions, updated during mutator time. At the start of gc its value is copied to `G1CollectionSet::_bytes_used_before`, and then never touched again. The `_bytes_used_before` is read at end of gc, and then reset.
> 
> This change simply removes `_inc_bytes_used_before` and directly uses `_bytes_used_before` to accumulate eden region used bytes.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into pull/12113
 - ayang review, remove redundant _bytes_used_before
 - initial version

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Changes: https://git.openjdk.org/jdk/pull/12113/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12113&range=02
  Stats: 57 lines in 5 files changed: 2 ins; 52 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12113.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12113/head:pull/12113

PR: https://git.openjdk.org/jdk/pull/12113