#11713 Remove historical docs from RTD

[JudgeGregg]

Scope and purpose

Fixes #11713
Remove historical docs from RTD since it can confuse Twisted users.

Add any comments about trade-offs (if any) made in this PR and the reasoning behind them:
We lose "history" but it's available in the repo and internet archives:

#11684 (comment)

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[JudgeGregg]

please review

[adiroiban]

Thanks for the cleanup.

I have created this repo https://github.com/twisted/historic

For which the files are available at https://twisted.org/historic/

If you have time, I have added you to that repo.
Can you copy these removed files there?

In this way, there is still a way to check them... if needed
and we can add a redirection rule later for twisted.org