layers: Remove unused threadchecker header file
layers: Remove unused threadchecker header file

Change-Id: I7906b82c1c9c0397113508da74348ea28fe21add

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