ci: drop "eslint-plugin-prettier" dependency

[justinmk]

Problem

raised in #437 (comment) by @mikavilpas

[prettier] being run as part of eslint is an older way and nowadays not recommended.

And https://prettier.io/docs/en/integrating-with-linters.html confirms that. Instead it recommends running prettier --check explicitly.

Proposal

drop the "eslint-plugin-prettier" dependency if (and only if) we can achieve the same functionality we have today, which is that we have one "lint" task and one way to auto-fix lint issues.

• one npm run lint command that runs prettier --check + eslint
• one npm run fixlint command that fixes prettier issues + eslint issues

[justinmk]

#447