Use correct allocator in debug_utils.c

Use correct allocator in debug_utils.c

loader_calloc_with_instance_fallback is used in places where a user can
supply their own allocator, but should default to the allocator used with
the instance otherwise. The issue was that loader_free was being used with
objects created with the instance allocator, but loader_free only takes the
user provided one, leading to leaks.