Revert "media/gpu: Support VP9 resolution changes to smaller w/o dropping ref frames"

This reverts commit 2c14d4b2f528aacadfe4e48740a733141b9ece4c.

Reason for revert: Started regression tracked in b:262058997

Original change's description:
> media/gpu: Support VP9 resolution changes to smaller w/o dropping ref frames
>
> VA-API VideoDecoders support resolution changes mid-stream to smaller
> (without a keyframe), however VP9Decoder thinks this is not supported
> and drops all the reference frames, causing some WebM test vector
> MD5SUMs to fail.
>
> This CL adds a parameter to VP9Decoder to avoid dropping said reference
> frames when the resolution change is to a smaller one, and sets it to
> true from VaapiVideoDecoder only.
>
> Tested on Intel (TGL volteer) and AMD (guybrush).
>
> Bug: b:207057398
> Change-Id: I21c50795ba26732b91563255330d79eb1168835d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4032552
> Reviewed-by: Andres Calderon Jaramillo <andrescj@chromium.org>
> Commit-Queue: Miguel Casas-Sanchez <mcasas@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1074245}

Bug: b:207057398
Change-Id: I39ccf0239b8a2202de27fa14934cff451eab4d72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4205690
Reviewed-by: Miguel Casas-Sanchez <mcasas@chromium.org>
Commit-Queue: Miguel Casas-Sanchez <mcasas@chromium.org>
Auto-Submit: Drew Davenport <ddavenport@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1098997}

• media/gpu/vaapi/vaapi_video_decoder.cc[diff]
• media/gpu/vaapi/vaapi_video_decoder.h[diff]
• media/gpu/vp9_decoder.cc[diff]
• media/gpu/vp9_decoder.h[diff]