Revert "a11y-common-mv3: Add MV3 test variations"

This reverts commit be763f950c79a4702b207f8fd1530c7964fddb11.

Reason for revert: ManifestV3/FaceGazeIntegrationTest tests failing on Linux ChromiumOS MSan Tests
https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests/53481/overview

Bug: 388867838
Original change's description:
> a11y-common-mv3: Add MV3 test variations
>
> - Add MV3 variations to accessibility common browser tests.
> - Allow browser-shutting-down extension error during DictationTest
>   shutdown because MV3 service workers are not stopped at the same
>   timing as MV2 background pages and dictation has event listeners
>   that make extension api calls during shutdown.
>
> AX-Relnotes: n/a.
> Bug: 388867838
> Change-Id: I04bcf364a38b04653baaf1b02866c6a7aab5bff0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6713990
> Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
> Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1484428}

Bug: 388867838
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I0e5051852aafdae61dfaa93c390b8472d1e3bb76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6719773
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Owners-Override: Keishi Hattori <keishi@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1484773}