openssl: exclude more dangerous environment variables

[trws]

Minimal set of environment variables added to be cleared for the openssl package, these are used as control variables by openssl and can easily cause configuration and build failures if let through. This is a stopgap while we wait on #30015.

[spackbot-app]

Hi @trws! I noticed that the following package(s) don't yet have maintainers:

• openssl

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    maintainers = ['trws']

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$ spack blame openssl

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[haampie]

is this not something you can do in setup_build_environment?

[trws]

It is, the PR to do this more completely all over the place does that in build_environment's clean stuff in fact, but I put this where it is because that's where the only existing environment cleaning was happening in the package.