anki: remove pip from anki-build-python

[tjni]

Description of changes

I am trying to fix this failure on the python-updates branch, which is testing some changes that includes updating pip:

error: collision between `/nix/store/n3kxpnlhnbcm46xnkf6zka704darazzz-python3-3.10.12-env/bin/pip3.10' and `/nix/store/n9jd7i76x2vcgp5l5imaa1141mi05s4p-python3.10-pip-23.2.1/bin/pip3.10'

I am not sure why it doesn't happen currently. I'm not able to test the behavior of the application, because I'm on macOS, but I have been able to verify it still builds on aarch64-linux. If anyone is able to better test this, please do!

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/)
• 23.11 Release Notes (or backporting 23.05 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
• Fits CONTRIBUTING.md.

[euank]

I verified it still builds and runs on x86 linux just fine for me.

Thanks!