Revert "Disable AAC WebCodecs tests on Nexus 5X bots"

This reverts commit c90da1635d4a84bc5afec453592825fd62788855.

Reason for revert: A fix has landed here:
https://chromium-review.googlesource.com/c/chromium/src/+/5003325

Original change's description:
> Disable AAC WebCodecs tests on Nexus 5X bots
>
> The Nexus 5X bots are failing since the WebCodecs AAC encoding tests
> were enabled. Turn them off to avoid noise.
>
> Bug: 1498663
> Change-Id: I12b4dcdf37dfccb603c7e9b4dbbd362108717f37
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5002990
> Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
> Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
> Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
> Auto-Submit: Thomas Guilbert <tguilbert@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1219177}

Bug: 1498663
Change-Id: Ib312b3702400f1986904d9658da7fd67b46d6fd7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5005241
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1219587}