refactor: remove commons beanutils

[BobDu]

Testing done

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[basil]

Isn't this just inlining it rather than removing it? Which means we have the maintenance version of maintaining the inlined copy. Plus we wouldn't be able to remove the BeanUtils JAR from Jenkins core either, because it's used by Stapler/Jelly.

[BobDu]

I also discovered this issue during further exploration.

Let's wait and see if apache/commons-beanutils#359 is accepted.