RFR: 8369793: G1: Remove unused G1FreeIdSet [v2]

[Thomas Schatzl]

> Hi all,
> 
>   please review this trivial removal of the unused `G1FreeIdSet` code. JEP 522 made it obsolete.
> 
> Testing: local compilation, gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  * also remove gtest

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/27786/files
  - new: https://git.openjdk.org/jdk/pull/27786/files/0850d7d9..537b137b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27786&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27786&range=00-01

  Stats: 163 lines in 1 file changed: 0 ins; 163 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27786.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27786/head:pull/27786

PR: https://git.openjdk.org/jdk/pull/27786