RFR: 8298469: Obsolete legacy parallel class loading workaround for non-parallel-capable class loaders

[Coleen Phillimore]

This change removes the JVM code and option (default off) to synchronize class loading for non-parallel capable class loading.  For more information see: https://bugs.openjdk.org/browse/JDK-8295673
and Release Note for the option in 20: https://bugs.openjdk.org/browse/JDK-8296446

Now Release Note for removal: https://bugs.openjdk.org/browse/JDK-8303967

Tested with tier1-7.

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

Commit messages:
 - 8298469: Obsolete legacy parallel class loading workaround for non-parallel-capable class loaders

Changes: https://git.openjdk.org/jdk/pull/12974/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12974&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298469
  Stats: 163 lines in 10 files changed: 1 ins; 147 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/12974.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12974/head:pull/12974

PR: https://git.openjdk.org/jdk/pull/12974