layers: Clean up old mem_tracker merge remnants
layers: Clean up old mem_tracker merge remnants

Clean up most of the remaining MTMERGESOURCE defines.
Many of these come straight out. A number of copy functions
were able to merge some code to provide a slight efficiency gain.

Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,critsec/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,elongbug/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,KhronosGroup/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,KhronosGroup/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers