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.

sys/msdos/vidvesa.c

@@ -596,7 +596,7 @@ vesa_cl_eos(int cy)
 }
 
 void
-vesa_tty_end_screen(void)
+vesa_term_end_screen(void)
 {
     vesa_clear_screen(BACKGROUND_VESA_COLOR);
     vesa_SwitchMode(MODETEXT);