Revert "Move KeyedService dependency from unexportable_keys"

This reverts commit 1c471915c32529e19b3df148a7664f06e2684831.

Reason for revert: Breaks tests on linux-ubsan-vptr, see https://ci.chromium.org/ui/p/chromium/builders/ci/linux-ubsan-vptr/30215/overview

Original change's description:
> Move KeyedService dependency from unexportable_keys
>
> This is needed as net/ does not have a concept of profiles,
> and cannot use unexportable_keys with this dependency.
>
> Created a wrapper in chrome/browser/signin to handle
> KeyedService as it is not needed in other places.
>
> Bug: 41495201
> Change-Id: I6a39acefce2cce8a1658302756605c41afddd34e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5550652
> Auto-Submit: Kristian Monsen <kristianm@chromium.org>
> Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
> Reviewed-by: Alex Ilin <alexilin@chromium.org>
> Commit-Queue: Alex Ilin <alexilin@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1304916}

Bug: 41495201
Change-Id: I834d796bbc26b7b806ce46b0382dbc422884559d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5563144
Owners-Override: Marc Treib <treib@chromium.org>
Auto-Submit: Marc Treib <treib@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1305027}