layers:Remove "using namespace std" statement
layers:Remove "using namespace std" statement

Remove "using namespace std;" statement from core validation. This is
prohibited in the coding standard. Replace with specific "using"
statements for the parts of std that we use.

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