RFR: 8149: Cleanup project files after JMC-7307

Sat Dec 2 00:01:20 UTC 2023

[JMC-7307](https://bugs.openjdk.org/browse/JMC-7307) moved org.openjdk.jmc.flightrecorder.configuration to core. After that, there are a few plugin related files that are obsolete.

Also, with latest Eclipse there are some changes in the .classpath files that get generated, e.g. when reimporting Maven projects. We should clean this up and unify .classpath files.

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Commit messages:
 - JMC-8149

Changes: https://git.openjdk.org/jmc/pull/534/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=534&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8149
  Stats: 330 lines in 24 files changed: 210 ins; 112 del; 8 mod
  Patch: https://git.openjdk.org/jmc/pull/534.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/534/head:pull/534

PR: https://git.openjdk.org/jmc/pull/534