layers: Tweak comments for swapchain checks to be less brittle
layers: Tweak comments for swapchain checks to be less brittle

Referring to specific lines within an expression breaks every time this
code changes.

Signed-off-by: Chris Forbes <c3279c50043e18e9442c1ae071cafa0e7a4ca967@google.com>

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