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outdated/win/gem/wingem.c

@@ -69,8 +69,7 @@ struct window_procs Gem_procs = {
     Gem_get_color_string,
 #endif
 
-    /* other defs that really should go away (they're tty specific) */
-    Gem_start_screen, Gem_end_screen, Gem_outrip, Gem_preference_update,
+    Gem_outrip, Gem_preference_update,
     genl_getmsghistory, genl_putmsghistory
                             genl_status_init,
     genl_status_finish, genl_status_enablefield, genl_status_update,
@@ -523,16 +522,6 @@ Gem_resume_nhwindows()
 {
 }
 
-void
-Gem_end_screen()
-{
-}
-
-void
-Gem_start_screen()
-{
-}
-
 extern void mar_exit_nhwindows(void);
 extern boolean run_from_desktop;