Docs: update to past tense now pip 21.0 is out

[hugovk]

pip 21.0 has been released, dropping support for Python 2.7 🚀

Update the docs to past tense, for example:

-pip 21.0, in January 2021, will remove Python 2 support
+pip 21.0, in January 2021, removed Python 2 support

[uranusjr]

Hmm, I was thinking this does not need a changelog entry, but maybe it’s better to have one indicating the 21.0 release does not include this change and contains an error in the documentation.

[hugovk]

I'd probably just go for trivial, the docs are understandable without the change.

But happy to add a changelog if desired!

[pradyunsg]

It’d be possible to merge and make a 21.0.1 too.

[pfmoore]

Is this going to get merged soon? 21.0.1 could be getting released this weekend (depending on other factors). I won't delay the release for this, though...

[uranusjr]

Let’s do this in 21.0.1 then? This is not really that contriversial.