RFR: CODETOOLS-7902844: JMH: Clean up jmh.separateClassLoader support

[Aleksey Shipilev]

SonarCloud instance reports the following trouble in ClassUtils.loadClass: "Use try-with-resources or close this "URLClassLoader" in a "finally" clause."

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Commit messages:
 - CODETOOLS-7902844: JMH: Clean up jmh.separateClassLoader support

Changes: https://git.openjdk.java.net/jmh/pull/30/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmh&pr=30&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902844
  Stats: 70 lines in 2 files changed: 66 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jmh/pull/30.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh pull/30/head:pull/30

PR: https://git.openjdk.java.net/jmh/pull/30