In T93382, the problem was that the Blender-side rendering code was
still generating the subsurface passes because the old render pass
flags were set, even though Cycles doesn't generate them anymore.

After a closer look, it turns out that the entire hardcoded pass
creation code can be removed. We already have an Engine API function
to query the list of render passes from the engine, so we might as
well just call that and create the returned passes.

Turns out that Eevee already did this anyways. On the Cycles side, it
allows to deduplicate a lot of BlenderSync::sync_render_passes.
Before, passes were defined in engine.py and in sync.cpp. Now, all
passes that engine.py returns are created automatically, so sync.cpp
only needs to handle a few special cases.

I'm not really concerned about affecting external renderer addons,
since they already needed to handle the old "builtin passes" in
their Engine API implementation anyways to make them show up in the
compositor. So, unless they missed that for like 10 releases, they
should not notice any difference.