VP9 per layer settings should not force denoising.

In r36379 a change to per-resolution setting of denoising was introduced
that unintentionally enabled denoising on lower resolutions in the case
that VideoCodec::VP9()->denoising was false.
The CL makes sure the per-resolution setting are only allowed to
disable denoising, not enable it.

Bug: webrtc:13888
Change-Id: Ice07a5a7d27798dc2182a40af0ec521bde6210b6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/257303
Reviewed-by: Ying Wang <yinwa@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36412}