Remove the 'prettier' pre-commit hook

[sirosen]

Rationale:

• the mirror repo is archived
• the last human-driven maintenance involving this hook was in late
  2022 (2.5 years ago at time of writing)
• the hook itself behaves in an unstable way, repeatedly reformatting
  the same bits of markdown content
  (see: [pre-commit.ci] pre-commit autoupdate #2194)
• the hook was introduced to format MD, TOML, JSON, and YAML content,
  and better solutions exist for each of these formats
  • JSON: we can use the hook from pre-commit-hooks
  • TOML: we only have pyproject.toml, we can use the tox-dev hook
  • MD: it is better to do nothing; offers questionable value
  • YAML: we could use ruamel.yaml.cmd; offers questionable value

Contributor checklist

• Included tests for the changes.
• PR title is short, clear, and ready to be included in the user-facing changelog.

Maintainer checklist

• Verified one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).