refactor(faq): use consistent examples

[Squiddleton]

Please describe the changes this PR makes and why it should be merged: The original section for "How do I unban a user?" uses <CommandInteractionOptionResolver>.get(...).value instead of <CommandInteractionOptionResolver>.getUser(...) which is inconsistent with the nearby section regarding banning users. This corrects that, and it rewrites the tip that was originally based on message commands instead of slash commands.