We still keep a dummy BufferBuilder object around so that it can be used
for the builder error callback tests of the wire.
Change-Id: If0c502bb8b62ee3ed61815e34e9b6ee6c03a65ef
BindGroup usage isn't something that's part of WebGPU's sketch.idl and
it might never exist. Remove it to simplify the migration of bindgroup
to descriptor.
Change-Id: I21e0a98eb60434d4009e748cd9afcbf89edd7e6a