remove ctx.update_multiplicity

src/twn_engine_context_c.h

@@ -72,11 +72,6 @@ typedef struct EngineContext {
     SDL_Window *window;
     uint32_t window_id;
 
-    /* this should be a multiple of the current ticks per second */
-    /* use it to simulate low framerate (e.g. at 60 tps, set to 2 for 30 fps) */
-    /* it can be changed at runtime; any resulting logic anomalies are bugs */
-    uint32_t update_multiplicity;
-
     bool is_running;
     bool window_size_has_changed;
     bool resync_flag;