Remove kActiveDirectory type from account.h

Remove kActiveDirectory from the AccountType enum in account.h. Also
update the files where this enum value was still used.

This is a follow up to the following CL, in which we removed
ACCOUNT_TYPE_ACTIVE_DIRECTORY from tokens.proto:
https://chromium-review.googlesource.com/c/chromium/src/+/6207096

This is one of the final steps for removing Chromad-related code from
ChromeOS (see crbug.com/263367348 for additional context).

Bug: 291783005
Change-Id: I83ef5198ef0ae31984ba5b97610a3f87eb7dec86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6226680
Auto-Submit: Felipe Andrade <fsandrade@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1417489}