layers: Clean up layer settings file comments.
layers: Clean up layer settings file comments.

Normalize and clean up internal documentation for the
vk_layer_settings.txt file.
No logic or behavior changes.

Change-Id: Iceb45efb50bcb670b099027980244cc1e2358643

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools