RFR: 8374048: Genshen: Backout fix for missed cancellation notice

[William Kemper]

The "fix" for the relatively infrequent bug: https://bugs.openjdk.org/browse/JDK-8373100, is causing a frequent `nullptr` error. We are backing out the problematic fix while we work on a better solution.

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Commit messages:
 - Revert "8373100: Genshen: Control thread can miss allocation failure notification"

Changes: https://git.openjdk.org/jdk/pull/28910/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28910&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374048
  Stats: 23 lines in 2 files changed: 8 ins; 4 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/28910.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28910/head:pull/28910

PR: https://git.openjdk.org/jdk/pull/28910