layers: Use unique_ptr for descriptor set layout map
layers: Use unique_ptr for descriptor set layout map

This fixes a leak where PostCallRecordDestroyDescriptorSetLayout erases
from the map without calling delete on the erased element.

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