layers: Remove old/unnecessary FIXME from swapchain layer
layers: Remove old/unnecessary FIXME from swapchain layer

This FIXME comment does not apply.  It may have applied, if the line being
referred to once copied a pointer to user data, but at this point, the actual
data is being copied into a struct owned by the swapchain layer, which is what
the comment was about.

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