Revert "[webauthn] Update dialog focus behaviour"

This reverts commit b03aa6bffded0c7769eb5000db1642d78bc24ec6.

Reason for revert: breaks keyboard navigation on linux.

Second attempt at reverting this CL.

Original change's description:
> [webauthn] Update dialog focus behaviour
>
> This CL updates the focus behaviour of webauthn dialogs. Previously, the
> "primary" control of each sheet was focused, which was either a list of
> options or one of the buttons. This behaviour was problematic for screen
> readers:
>
> First, it is not recommended to jump to a button that is most likely not
> what the user wants to do at a given moment [1]. E.g. on the security
> key activation dialog, the user most likely wants to tap their security
> key, not cancel out of the dialog.
>
> Second, the authenticator dialog is special because its contents change
> as the user interacts with the authenticator, but the container itself
> does not. The resulting behaviour is that screen readers will read
> whatever gets focused next but will not announce the new context. This
> is really confusing, e.g. if the request times out, VoiceOver on Mac
> would announce "Cancel - Button" instead of "The request timed out...".
>
> This CL addresses these issues by making the title of the dialog
> accessibility-focusable and focusing it every time the sheet is updated.
> The modal is still keyboard navigable, with the enter key triggering the
> default button if present.
>
> [1] https://www.w3.org/WAI/ARIA/apg/patterns/dialog-modal/
>
> Bug: 1347607
> Change-Id: If59fbd8f2dbfa3eb7a554d6ecd5ad82df29f2879
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4894369
> Commit-Queue: Nina Satragno <nsatragno@chromium.org>
> Commit-Queue: Adam Langley <agl@chromium.org>
> Auto-Submit: Nina Satragno <nsatragno@chromium.org>
> Reviewed-by: Adam Langley <agl@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1202832}

Bug: 1347607
Change-Id: If2019823cf1de1b770f06fa0028aa7ef791d98e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4902478
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Nina Satragno <nsatragno@chromium.org>
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1203626}