layers: On Free/Destroy fix unique_objects map cleanup
layers: On Free/Destroy fix unique_objects map cleanup

When an object is freed or destroyed, unique_objects must clean up its
map entry prior to calling down the chain. This is becase the ICD may
be preempted just after object deletion, and the same object handle
could then be allocated before returning to validation. In that case,
unique_objects would delete the entry for the newly-created object.

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