Clean out main requirements.txt

[cowlicks]

Most packages inside /requirements.txt seem to only be used in /test/rules so move those things to /test/rules/requirements.txt.

The exception is lxml and selenium.

The selenium requirement will be removed in #12624

[https-everywhere-bot]

Hey, I couldn't find the type of issue in your description. Can you edit your issue to add this (perhaps referring to the issue template?)

[Bisaloo]

@Hainish, you fixed this in b008ed1, can you close this issue please?