Remove python integration test in-the-past scaffolding

[aarongable]

Remove the "setup_six_months_ago" and "setup_twenty_days_ago" scaffolding in our python integration test harness, which (with the removal of the last OCSP tests) no longer has any users. This simplifies that python code and reduces integration test runtime by about 30 seconds.

Part of #4934

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Warning

Do not merge until #8344 has been merged

[jsha]

I like the idea of saving 30 seconds on our integration tests, and I agree that this code is stable and going away soon with the removal of OCSP services. But we shouldn't land this before the actual removal of OCSP services, since we are still responsible for correct operation until then. Let's hold this PR until that happens. Other than the question of timing, looks good.

Also lol that setup_six_months_ago() uses a list comprehension and setup_twenty_days_ago() uses a for loop even though they do the exact same thing and are very close to each other. :D

[jsha]

Looks good. It appears there is also an uncalled get_future_output that we could remove.

I assume we'll also remove the FAKECLOCK support in Boulder itself as a followup to this?

[aarongable]

Good point! I'll do both of those in a followup: #8356

The base branch was changed.