doc: revise objections section of collaborator guide

The bold text is overused in this section. This change removes it. It also changes some wording: PR -> pull request, can -> may in a rare instance where "may" is the right choice in our docs, etc. (The recommendation to avoid "may" is because "may" implies permission rather than just ability. Yes, I'm probably the one that changed it from "may" in the first place.)