nose: clean up, support Python 3.10. (#8825)

Due to changes in setuptools, we need to run 2to3 ourselves.
While we're at it, lets apply relevant patches from Debian.

https://salsa.debian.org/python-team/packages/nose/

dev-python/nose/patches/debian/sphinx-body-max-width.diff

@@ -0,0 +1,22 @@
+From: Dmitry Shachnev <mitya57@debian.org>
+Date: Sat, 8 Feb 2020 13:12:45 +0300
+Subject: Unset body max-width option
+
+Sphinx 1.7+ sets it to 800px by default, which does not play nice with
+our right sidebar.
+---
+ doc/conf.py | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/doc/conf.py b/doc/conf.py
+index 358414f..cccfd95 100644
+--- a/doc/conf.py
++++ b/doc/conf.py
+@@ -199,6 +199,7 @@ html_theme_options = {
+     'relbarbgcolor': '#fff',
+     'relbartextcolor': '#20435c',
+     'relbarlinkcolor': '#355f7c',
++    'body_max_width': None,
+ }
+ 
+ # the css mostly overrides this: