[media] Remove legacy multiplanar codepath from VideoResourceUpdater

Remove legacy multiplanar codepath from VideoResourceUpdater that
has UseWritePixelsYUV enabled in M127 and has shipped for quite some
time.

Added couple TODOs to simplify/remove more plane-related code later.

Bug: 332564976
Change-Id: I48c6c25dca1ef043c8b59e278c1946795ff5f952
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5798528


Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Saifuddin Hitawala <hitawala@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1345050}