RFR: 8315869: UseHeavyMonitors not used

[Coleen Phillimore]

Please review this trivial change to remove the UseHeavyMonitors develop option, in favor of the now non-experimental LockingMode=LM_MONITOR (0) option.  Tested with tier1 locally.

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Commit messages:
 - 8315869: UseHeavyMonitors not used

Changes: https://git.openjdk.org/jdk/pull/15845/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15845&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315869
  Stats: 16 lines in 4 files changed: 0 ins; 13 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15845.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15845/head:pull/15845

PR: https://git.openjdk.org/jdk/pull/15845