Also deletes tons of fixed-function-centric stuff that will never be
used by the Vulkan backend. Very little of the SPIRV integration
actually does anything interesting yet (we don't generate code) but this
wires on the new shader representation.

Bug: b/120799499

Change-Id: Ib76e2086113098aebd526a0da461689d4344e8c2
Reviewed-on: https://swiftshader-review.googlesource.com/c/23090Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>