[session] drop pre-3.7 api on session
Dropping of API deprecated since 3.7 decided in #2772958
importConfigParsertry:undo_actions=config.cfgfile_parser.get('MAIN','undo-support',False)exceptConfigParser.NoOptionError:pass# this conf. file was probably already migratedelse:config.global_set_option('undo-enabled',bool(undo_actions))