Revert "[Tab Groups Sync] Calculate tab positions on browser startup"

This reverts commit 5dce36603f0bda397f38ffc1c5d3cc3459d84c77.

Reason for revert: First failed/flaky build https://ci.chromium.org/ui/p/chromium/builders/ci/android-12-x64-rel/12356/overview

Original change's description:
> [Tab Groups Sync] Calculate tab positions on browser startup
>
> This CL sorts the stored entries by their unique positions and uses the
> sorted order to calculate tab positions.
>
> Integer positions are not used to avoid storing all the tabs in a group
> if only one tab was moved (because positions of all the following tabs
> would be changed).
>
> Raw sync metadata is used instead of sync processor's API to extract
> unique positions because ModelReadyToSync() is expected to be called
> when the model is initialized. ModelReadyToSync() may internally clear
> sync metadata and call SpplyDisableSyncChanges().
>
> Bug: 351357559
> Change-Id: Iad613b896a11925e3e58a6431eb230f8f902c8d7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5929123
> Reviewed-by: Mikel Astiz <mastiz@chromium.org>
> Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
> Commit-Queue: Rushan Suleymanov <rushans@google.com>
> Cr-Commit-Position: refs/heads/main@{#1368411}

Bug: 351357559
Change-Id: I7d12f24a9d9af0e6e211a7b5c14338ef5f218b82
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5934543
Commit-Queue: Rubin Deliallisi <rubindl@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Rubin Deliallisi <rubindl@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1368678}