RFR: 8289: Remove security manager related code [v2]

[Alex Macdonald]

On Wed, 23 Apr 2025 23:56:37 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> Cherry picked my changes into a new branch.
>
> Marcus Hirt has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixing unused imports

Looks okay to me, just needs a `mvn spotlesss:apply` run to clean up the checkstyle warnings

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PR Review: https://git.openjdk.org/jmc/pull/642#pullrequestreview-2791429249