RFR: 8344797: GenShen: Update and rename confusing method [v2]

[William Kemper]

> A few riders here:
> * [Remove vestigial debugging assertions](https://github.com/openjdk/shenandoah/commit/9062113458bd1909409967abb743e11982f351ab)
> * [Log cancellation time at debug level](https://github.com/openjdk/shenandoah/commit/e3dd23efcb179bc61565d25f6b46f3690a50caa4)
> * [Use try_set instead of set](https://github.com/openjdk/shenandoah/pull/550/commits/49cb66a0fa7d0d660f5b986eea9d71035c157310)

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

  Only get elapsedTime for debug log message when debug logging is enabled

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/550/files
  - new: https://git.openjdk.org/shenandoah/pull/550/files/49cb66a0..978283fa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=550&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=550&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/550.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/550/head:pull/550

PR: https://git.openjdk.org/shenandoah/pull/550