Blender Git Loki

Cycles: Remove passes from BufferParams

Now it is the Scene which is the source of truth for passes.

The RenderBuffers will store pre-calculated offsets and strides
which are set once when the passes are known. There are few things
which are good:

- Data is no longer duplicated, is clear where passes are to be
accessed from.
- Code which sues BufferParams can access offsets and strides
directly, without re-calculating anything.
- DenoiserBuferParams are removed, since it does not bring any
new functionality.

Some downsides:

- Construction of new RenderBuffers is to be done with a bit more
care now.

- Passes needs to be passed to `get_pass_rect`.
A bit annoying, and almost like the RenderBuffers is the wrong place
for this function.

- `set_pass_rect` is disabled for now. Is unclear whether it will be
needed in the future, and what would it final placement be.