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.

win/tty/termcap.c

@@ -505,7 +505,7 @@ tty_ascgraphics_hilite_fixup(void)
 #endif /* PC9800 */
 
 void
-tty_start_screen(void)
+term_start_screen(void)
 {
     xputs(TI);
     xputs(VS);
@@ -537,7 +537,7 @@ tty_start_screen(void)
 }
 
 void
-tty_end_screen(void)
+term_end_screen(void)
 {
     term_clear_screen();
     xputs(VE);