Remove unused or useless SDL_Rects from Graphics

These were bfont_rect, bg_rect, foot_rect, and images_rect.

bg_rect was only used once to draw the ghost buffer in the editor, but
that was only because Ally didn't know you could just pass NULL in, cuz
the ghost buffer is the same size as the backbuffer.

desktop_version/src/Editor.cpp

@@ -929,7 +929,7 @@ void editorrender(void)
                 BlitSurfaceColoured(graphics.sprites[ed.ghosts[i].frame],NULL, graphics.ghostbuffer, &drawRect, graphics.ct);
             }
         }
-        SDL_BlitSurface(graphics.ghostbuffer, NULL, graphics.backBuffer, &graphics.bg_rect);
+        SDL_BlitSurface(graphics.ghostbuffer, NULL, graphics.backBuffer, NULL);
     }
 
     //Draw Cursor