Simplify workflow for feedback-reminder

[snicoll]

When an issue is waiting for feedback with a reminder and someone outside the team comments on the issue, the bot removes both the waiting-for-feedback and feedback-reminder labels.

For the clock to restart, a team member must set both the waiting-for-feedback and feedback-reminder labels. If the feedback reminder label only is added, nothing really happens. This has been a source of confusion in the past, see spring-projects/spring-framework#32995 for instance.

I wonder if adding the feedback-reminder only led the bot to add the waiting-for-feedback as it needs it to operate properly. I don't know what the GitHub API lets us to do but I also wonder if re-adding the waiting-for-feedback only shouldn't add the reminder if the bot is able to figure out it was in that state.

cc @bclozel

[wilkinsona]

See also #23. I think it may be time to consider some broader revisions to how the feedback labels are managed by the bot.