RFR: 8320602: Lock contention in SchemaDVFactory.getInstance()

[Joe Wang]

Applying an update from the upstream source, quote: "Removing synchronized from the getInstance() methods". As the reporter noted, this change was made 16 years ago.

Tests: SQE & unit tests passed

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Commit messages:
 - 8320602: Lock contention in SchemaDVFactory.getInstance()

Changes: https://git.openjdk.org/jdk/pull/16829/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16829&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320602
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16829.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16829/head:pull/16829

PR: https://git.openjdk.org/jdk/pull/16829