python{27,310}Packages.deprecation: remove unittest2, break on Python 2

[tjni]

Description of changes

The deprecation package makes use of features from unittest only available since Python 3.4, but it also supports Python 2.7. It uses unittest2, which backports those features. Discussion about this is in briancurtin/deprecation#54.

We'd like to stop packaging unittest2 it since it is unmaintained and caused us some pain on Python 3.10, so we apply briancurtin/deprecation#57.

In the first commit, this PR applies the patch unconditionally (eating the rebuilds, since it's unclear if it will be accepted and released upstream) and also hides the unittest2 requirement inside of a python2-modules override.

In the second commit, this PR removes the python2-modules override, explicitly choosing to drop support for it in Python 2.

Related to #154264 and #154650.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[SuperSandro2000]

Why do we want to target staging?

[tjni]

This was my bad, I assumed there would be more rebuilds than there were. I've retargeted the PR to master.

[dotlambda]

hides the unittest2 requirement inside of a python2-modules override

No need to add that override. Python 2 (especially python2Packages) us no longer maintained.

[tjni]

@dotlambda Thanks for your review. I pushed an additional commit removing the override. I prefer to keep the two commits separate, as they each have their own purpose, but this should achieve what you want to see.