openssl@3: depend on ca-certificates

[carlocab]

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This change aligns the formula with OpenSSL 1.1. See #86304.

Also, make this keg-only on Linux too while we're still primarily using
openssl@1.1.

[Bo98]

While we're here, can we remove enable-md2? We should not be supporting that going forward (but could keep it in 1.1 for compatibility reasons).

[carlocab]

Sure, done.

[BrewTestBot]

🤖 A scheduled task has triggered a merge.