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/2to3-fixups.diff

@@ -0,0 +1,66 @@
+From: Dmitry Shachnev <mitya57@debian.org>
+Date: Sat, 30 Oct 2021 20:54:36 +0300
+Subject: Remove code that relied on setuptools calling 2to3
+
+Setuptools no longer runs that, we run 2to3 from debian/rules.
+---
+ setup.cfg    |  1 -
+ setup.py     | 12 ------------
+ setup3lib.py |  2 +-
+ 3 files changed, 1 insertion(+), 14 deletions(-)
+
+diff --git a/setup.cfg b/setup.cfg
+index 9e927a5..308e4de 100644
+--- a/setup.cfg
++++ b/setup.cfg
+@@ -2,7 +2,6 @@
+ with-doctest = 1
+ doctest-extension = .rst
+ doctest-fixtures = _fixtures
+-py3where = build/tests
+ 
+ [bdist_rpm]
+ doc_files = README.txt
+diff --git a/setup.py b/setup.py
+index 29e29a8..9499468 100644
+--- a/setup.py
++++ b/setup.py
+@@ -6,17 +6,6 @@ py_vers_tag = '-%s.%s' % sys.version_info[:2]
+ 
+ test_dirs = ['functional_tests', 'unit_tests', os.path.join('doc','doc_tests'), 'nose']
+ 
+-if sys.version_info >= (3,):
+-    import setuptools
+-
+-    extra = {'use_2to3': True,
+-             'test_dirs': test_dirs,
+-             'test_build_dir': 'build/tests',
+-             'pyversion_patching': True,
+-             }
+-else:
+-    extra = {}
+-
+ try:
+     from setup3lib import setup
+     from setuptools import find_packages
+@@ -36,7 +25,6 @@ try:
+     if sys.version_info.major == 2:
+         addl_args['entry_points']['console_scripts'].append(
+             'nosetests%s = nose:run_exit' % py_vers_tag)
+-    addl_args.update(extra)
+ 
+     # This is required by multiprocess plugin; on Windows, if
+     # the launch script is not import-safe, spawned processes
+diff --git a/setup3lib.py b/setup3lib.py
+index 27bdb93..51164b8 100644
+--- a/setup3lib.py
++++ b/setup3lib.py
+@@ -3,7 +3,7 @@ from setuptools import setup as _setup
+ 
+ py3_args = ['use_2to3', 'convert_2to3_doctests', 'use_2to3_fixers', 'test_dirs', 'test_build_dir', 'doctest_exts', 'pyversion_patching']
+ 
+-if sys.version_info < (3,):
++if True:
+     # Remove any Python-3.x-only arguments (so they don't generate complaints
+     # from 2.x setuptools) and then just pass through to the regular setup
+     # routine.