Revert "OOBE: Migrate GuestToS screen to Polymer3"

This reverts commit 9b6cd850772419cde61a7c4d0963b20b5b8ba2b8.

Reason for revert: Suspect for failures since

https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/18707

Many All/OobeInteractiveUITest.SimpleEndToEnd/* browser_tests failing like

2021-11-14T18:39:54.417444Z ERROR browser_tests[3568:3568]: [CONSOLE(1)] "Uncaught SyntaxError: Identifier 'EULA_TERMS_URL' has already been declared", source: chrome://oobe/screens/oobe/oobe_eula.js (1)

Original change's description:
> OOBE: Migrate GuestToS screen to Polymer3
>
> Bug: 1251576
> Change-Id: I0187b4843e022586390e4f23da9ac3b86f2a94a3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3269216
> Commit-Queue: Ossama Mahmoud <osamafathy@google.com>
> Reviewed-by: Roman Aleksandrov <raleksandrov@google.com>
> Reviewed-by: Renato Silva <rrsilva@google.com>
> Cr-Commit-Position: refs/heads/main@{#941510}

TBR=raleksandrov@google.com,chromium-scoped@luci-project-accounts.iam.gserviceaccount.com,rrsilva@google.com,osamafathy@google.com

Change-Id: I1bab8b8811bbdf4be552034e5c6e45cfcb5996f5
No-Presubmit: true
No-Tree-Checks: true
Bug: 1251576
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3279328
Owners-Override: Trent Apted <tapted@chromium.org>
Auto-Submit: Trent Apted <tapted@chromium.org>
Reviewed-by: Ben Reich <benreich@chromium.org>
Commit-Queue: Ben Reich <benreich@chromium.org>
Cr-Commit-Position: refs/heads/main@{#941538}