doc: revise Collaborator Guide on reverting

Revise the "Reverting commits" section of the Collaborator Guide. Reduce
passive voice. Increase clarity.

PR-URL: https://github.com/nodejs/node/pull/25942


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>