input: don't use recursive mutex

Previous commits made sure that the lock will never be called for more
than once for all public functions. Thus deadlock is impossible, so
recursive mutex is unneeded and can be converted to a normal mutex.

input/input.c

@@ -1351,7 +1351,7 @@ struct input_ctx *mp_input_init(struct mpv_global *global,
 
     ictx->opts = ictx->opts_cache->opts;
 
-    mp_mutex_init_type(&ictx->mutex, MP_MUTEX_RECURSIVE);
+    mp_mutex_init(&ictx->mutex);
 
     // Setup default section, so that it does nothing.
     mp_input_enable_section(ictx, NULL, MP_INPUT_ALLOW_VO_DRAGGING |