window-port updates

Remove start_screen() and end_screen() from the
Window-port interface.

They were only ever used by tty, and there was a comment
carried to several window-ports about how they "really
should go away. They are tty-specific"

term_start_screen() and term_end_screen() are part of
terminal/NO_TERMS supporting routines now.

outdated/sys/mac/macwin.c

@@ -3275,9 +3275,6 @@ struct window_procs mac_procs = {
     tty_change_color, tty_change_background, set_tty_font_name,
     tty_get_color_string,
 #endif
-    /* other defs that really should go away (they're tty specific) */
-    0, //    mac_start_screen,
-    0, //    mac_end_screen,
     genl_outrip, genl_preference_update, genl_can_suspend_no,
 };