Fix #135116: DRW: Leaks while using generated metarig rigs

In this case, the evaluator cache was never referenced and
the subdiv free queue empty. So the freeing of the cache
never happened.

This function is called once per frame and is unlikely
to generate overhead by doing one lock.

source/blender/draw/intern/draw_cache_impl_subdivision.cc

@@ -1997,10 +1997,6 @@ void DRW_subdiv_cache_free(bke::subdiv::Subdiv *subdiv)
 
 void DRW_cache_free_old_subdiv()
 {
-  if (gpu_subdiv_free_queue == nullptr) {
-    return;
-  }
-
   BLI_mutex_lock(&gpu_subdiv_queue_mutex);
 
   while (gpu_subdiv_free_queue != nullptr) {