RFR: 8302858: Polish FlightRecorderMXBeanImpl [v3]

[Kevin Walls]

On Mon, 20 Feb 2023 17:33:00 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes some polishing of the `FlightRecorderMXBeanImpl` class.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revoke key check

Updates look good 8-)

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PR: https://git.openjdk.org/jdk/pull/12656