De-duplicate "Game Saved" telesave textbox

The "Game Saved" text box, along with its associated telesave() call,
exists in both Game.cpp and Script.cpp, so one of them is the copy-paste
of the other. Unfortunately this copy-paste resulted in an inconsistency
where both of them don't check for the same things when deciding whether
or not the telesave should actually happen (this is why you don't
copy-paste, kids... it's scary!).

Either way, de-duplicating this now is less work for me later.

desktop_version/src/Game.h

@@ -133,6 +133,7 @@ public:
     void crewmate_textbox(const int r, const int g, const int b);
     void remaining_textbox(void);
     void actionprompt_textbox(void);
+    void savetele_textbox(void);
 
     void updatestate(void);