plain: ignore [commands] config We only have commands.{update,rebase}.requiredest so far. We should clearly ignore those two if HGPLAIN is in effect, and it seems like we should ignore any future config that will be added in [commands] since that is about changing the behavior of commands. Thanks to Yuya for suggesting to centralize the code in ui.py. While at it, remove the unnecessary False values passed to ui.configbool() for the aforementioned config options.