layers: Fix memleak of instance object in object tracker layer
layers: Fix memleak of instance object in object tracker layer

CreateInstance calls CreateObject for the instance. There was no
corresponding DestroyObject in DestroyInstance.

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers