Remove identity_manager/scope_set.h

Bug: 425896213
Change-Id: If6270b9393917f1e4873a06bf000fb8d20981546
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7264626
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Owners-Override: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Tanmoy Mollik <triploblastic@google.com>
Cr-Commit-Position: refs/heads/main@{#1562140}
NOKEYCHECK=True
GitOrigin-RevId: 66263c58fa0d6395ab1886eae13acca6bf97a25c