[docs] Clean up dead links in the docs

[Julien Palard]

Hi Ashwin, thanks for your work!

> I took some time to filter out all the links and check them using cURL
> with the script attached.

Here's what I got:

> https://pythonhosted.org/pyobjc/ 404

Found https://pypi.org/project/pyobjc/.

> https://www.jwz.org/doc/content-length.html 403
> https://www.jwz.org/doc/content-length.html 403
> https://www.jwz.org/doc/content-length.html 403

Only blocks curl, works with graphical user agents.

> http://www.catb.org/~esr/fetchmail/fetchmail-FAQ.html 000

Works for me.

> https://cnswww.cns.cwru.edu/php/chet/readline/rluserman.html#SEC9 000

Found https://tiswww.cwru.edu/php/chet/readline/rluserman.html#SEC9

> http://tcl.activestate.com/ 000

Found https://tcl.tk

> http://www.tldp.org/HOWTO/XML-RPC-HOWTO/index.html 000

Works for me.

> https://www.microsoft.com/com/ 404

Found https://docs.microsoft.com/en-us/windows/desktop/com/component-object-model--com--portal

> http://oldwiki.mingw.org/index.php/Python 0.000000e+00xtensions 404

Found http://www.mingw.org/wiki/FAQ#toc14

> http://catb.org/~esr/trove/ 000

Works for me.

> http://sphinx-doc.org/examples.html 404

Found http://www.sphinx-doc.org/en/master/examples.html

> https://hg.python.org/cpython/file/3.2/Misc/NEWS 504

Found https://github.com/python/cpython/blob/260a788767ff6dadd04ecf9e9e26b363ca28c8ae/Misc/NEWS

> https://parlab.eecs.berkeley.edu/wiki/_media/patterns/paraplop_g1_3.pdf 500

Found http://osl.cs.illinois.edu/media/papers/karmani-2009-barrier_synchronization_pattern.pdf

> http://greenteapress.com/semaphores/downey08semaphores.pdf 404

Found https://greenteapress.com/semaphores/LittleBookOfSemaphores.pdf

> http://hginit.com 000

Found https://www.mercurial-scm.org/wiki/QuickStart

I created a PR to reflect those changes here: https://github.com/python/cpython/pull/13491
You can proofread it :)

Bests,
-- 
Julien Palard
https://mdk.fr