layers: Remove CV imageToSwapchainMap
layers: Remove CV imageToSwapchainMap

This no longer served any purpose, and entries were never cleaned up
when swapchains were destroyed.

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