These were implemented using 64-bit and 128-bit accesses, respectively,
and thus cause both alignment and overflow issues. We weren't exposing
support for them, so they can be removed for now instead of requiring
an implementation which doesn't have these flaws.

According to https://vulkan.gpuinfo.org/listformats.php, R16G16B16 is
very rarely supported as an image format (but as a buffer format it is
fairly common). R32G32B32 is very widely supported actually, due to
being mandatory for Direct3D 10:
https://docs.microsoft.com/en-us/windows/win32/direct3ddxgi/format-support-for-direct3d-feature-level-10-0-hardware#dxgi_format_r32g32b32_typelesspcs-5

Bug: b/146387550
Change-Id: Ife0a1786a5228c872c3585403ab1ce47eafb4ce5
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51088
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>