- Fix mapping of B8G8R8A8 -- this is the same as the old D3DCOLOR.
- Remove all the other stream types that don't match anything in Vulkan.
- Remove unused resource pointer in stream

There is still future cleanup work to do here -- we should be able to
do vertex fetch purely based on the VkFormat rather than mapping it onto
the GL model.

Change-Id: Ia100ec68e8930acd17b6cba35a27403b4ef8e883
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/25768
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>