migrate request reviewers to github actions

[avivkeller]

This PR is the second half of https://github.com/nodejs/node/pull/53149 (and it can't be merged until after that). This removes the logic for requesting reviewers from the Github bot, as the functionality (if https://github.com/nodejs/node/pull/53149 is merged) will be moved to github actions.

[Trott]

Since this is dependent on another PR, I'm going to put it into draft mode so no one merges it prematurely.