RFR: 8336685: Shenandoah: Remove experimental incremental update mode [v2]

[William Kemper]

> Not a clean backport.
> 
> # Testing
> GHA, Dacapo, Extremem, Hyperalloc, Specjbb2015, Specjvm2008, Diluvian (with and without stress flags).

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Remove iu mode tests from ProblemList.txt

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

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/160/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/160/files/e4ee4511..c7894ea3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=160&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=160&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/160.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/160/head:pull/160

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/160