Remove line_rect and prect

`prect` just wasn't needed as it was used in one place, and
`line_rect` isn't used anymore.

desktop_version/src/Graphics.h

@@ -358,10 +358,8 @@ public:
 
     SDL_Rect tiles_rect;
     SDL_Rect sprites_rect;
-    SDL_Rect line_rect;
     SDL_Rect tele_rect;
 
-    SDL_Rect prect;
     SDL_Rect footerrect;
 
     int linestate, linedelay;