remove buehlmann(), setBuehlmann(bool)
buehlmann() is really planner_deco_mode == BUEHLMANN, so no need for a function
setBuehlmann is dangerous, because buehlmann is saved on disk, but not in prefs.* and thus can lead to inconsistency between bool buehlmann and planner_deco_moce.
Signed-off-by: Jan Iversen <jani@apache.org>