RFR: 8367107: JFR: Refactor policy tests out of TestRemoteDump

[Erik Gahlin]

Could I get a review of a PR that splits TestRemoteDump.java into two test files?

This change prevents timeouts and reduces wall clock time, as the tests can now run in parallel. As part of the change, I am reverting the modification to TestRemoteDump introduced with [JFR: Improve slow tests](https://bugs.openjdk.org/browse/JDK-8364756), which made the test flaky. I also removed unused imports and fixed the incorrect test summary.

Testing: 100 * (TestRemoteDump and TestDumpRetention)

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/27153/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27153&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367107
  Stats: 197 lines in 2 files changed: 123 ins; 73 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27153.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27153/head:pull/27153

PR: https://git.openjdk.org/jdk/pull/27153