layers: Remove now-redundant OT hdr prototypes
layers: Remove now-redundant OT hdr prototypes

Codegen creates its own prototypes, no longer need them in the header
file.

Change-Id: Ibaab124a26391dc4925e49f095ddac83523aa725

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