docs: Remove extra line in doc headers
docs: Remove extra line in doc headers

GitHub markdown adds a line after H1 and H2 entries.  Normal
markdown doesn't do this.  So my WSYIWYG editor incorrectly showed
the results of my previous edits.

Change-Id: I3c197c1fb1f364bf4b1050d1eaa1141affefe9d1

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