PRS: Remove text/plain, upload, and browse logic from pep2html.py

[AA-Turner]

Whilst we still need to maintain pep2html.py, having a large amount of dead code isn't useful. This is just removing unsed things, without refactoring anything else.

A

[CAM-Gerlach]

I'm -0 on this, since I don't really see the pressing need to strip out content and functionality that has been there nearly untouched for fully 20 years, when the script as a whole (now that PEP 676 should be pronounced on soon) should be retired within a couple months time at most, and to which any non-trivial further changes are effectively frozen anyway. While horribly unmaintainable, it doesn't really need to be maintained anymore, and I find it of historical value as a remarkably well-preserved time capsule into Python's past, so it might be fitting to retain that in the final version at the time it is removed. But perhaps I doth protest too much.

[hugovk]

Agreed, while is nice to see, I'd rather wait for the PEP decision and hopefully make it an even bigger minus!