RFR: 8327289: Remove unused PrintMethodFlushingStatistics option

[Sonia Zaldana Calles]

Hi all, 

This PR removes the option ```PrintMethodFlushingStatistics```. Last usage was removed in [8290025](https://bugs.openjdk.org/browse/JDK-8290025). 

Testing: 
- [x] Verified unrecognized VM option gets reported after patch. 

Thanks, 
Sonia

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Commit messages:
 - 8327289: Remove unused PrintMethodFlushingStatistics option

Changes: https://git.openjdk.org/jdk/pull/18903/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18903&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327289
  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18903.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18903/head:pull/18903

PR: https://git.openjdk.org/jdk/pull/18903