delete unused functions and signal for updating dbstop marker * main-window.h, main-window.cc (main_window::handle_update_dbstop_marker_request): Delete. (main_window::construct): Delete signal connection from _octave_qt_event_listener::update_dbstop_marker_signal to main_window::handle_update_dbstop_marker_request. * octave-qt-event-listener.h, octave-qt-event-listener.cc (octave_qt_event_listener::update_dbstop_marker): Delete. (octave_qt_event_listener::update_dbstop_marker_signal): Delete signal. * octave-event-listener (octave_event_listener::update_dbstop_marker): Delete.