Remove Features from registry

[loganek]

Registry doesn't have to keep track on the features, as they're only required within a timeline. I'd propose changing ht_timeline_set_feature() API to accept destroy callback, i.e.:

HT_API void ht_timeline_set_feature(HT_Timeline* timeline, size_t feature_type_id, void* feature, void(*destroy_feature)(void*));```