Revert "Add Android Desktop browser user policy registration type."

This reverts commit 9424c42242a99b048995993865920742e590b083.

Reason for revert: No longer need this new enum, will re-use existing BROWSER enum for Android Desktop

Bug: b:415793321
Original change's description:
> Add Android Desktop browser user policy registration type.
>
> Change-Id: I999992b2f22364b045b156d403aafa598d6fd9f8
> Bug: b:415793321
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6765985
> Reviewed-by: Victor Gabriel Savu <vsavu@google.com>
> Commit-Queue: Yanzhu Du <yzd@google.com>
> Cr-Commit-Position: refs/heads/main@{#1489647}

Bug: b:415793321
Change-Id: Id6fb31595abbc05b6b2c677aee377b0a751a4828
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6782058
Commit-Queue: Yanzhu Du <yzd@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Victor Gabriel Savu <vsavu@google.com>
Cr-Commit-Position: refs/heads/main@{#1491522}