demos: Remove DbgMsgs from incremental_present ext
demos: Remove DbgMsgs from incremental_present ext

The only DbgMsg messages left tell the user, if they use
"--incremental_present", whether the functionality is actually being
used, or if the VK_KHR_incremental_present extension isn't available.

NOTE: When somebody wants to see all of the DbgMsg messages, they should
use "git revert" with this commit.

Change-Id: Ic4189cbec2a64c50135b16c331c808fbbce975dc

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