[lilliput-jdk17u:lilliput] RFR: 8319778: Remove unreachable code in ObjectSynchronizer::exit

[Roman Kennke]

Backport of https://github.com/openjdk/jdk/commit/91279fcf058a6bb16a7749c328179ab94227bb8d

For cleanliness and easier subsequent backports. Almost clean, except a nullptr vs NULL diff.

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Commit messages:
 - 8319778: Remove unreachable code in ObjectSynchronizer::exit

Changes: https://git.openjdk.org/lilliput-jdk17u/pull/79/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk17u&pr=79&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319778
  Stats: 23 lines in 3 files changed: 0 ins; 22 del; 1 mod
  Patch: https://git.openjdk.org/lilliput-jdk17u/pull/79.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk17u.git pull/79/head:pull/79

PR: https://git.openjdk.org/lilliput-jdk17u/pull/79