Stop patching dh_virtualenv for Python 3.11+, now fixed

[legoktm]

The fixed dh_virtualenv version is now in Debian Bookworm, so we no longer need to patch it ourselves:

• https://tracker.debian.org/news/1418871/accepted-dh-virtualenv-122-13-source-into-unstable/
• https://tracker.debian.org/news/1420883/dh-virtualenv-122-13-migrated-to-testing/

Test plan

• [x] CI passes