[iOS] MutableProfileAttributesStorageIOS: Replace invalid CHECK

Before this CL, ProfileDeletionComplete() contained a CHECK to ensure
that the deleted profile was indeed marked for completion. That's
*usually* true but in one situation it's not: The profile deletion may
get triggered twice, and then on the second completion, the profile is
not marked for deletion anymore.

So this CL slightly weakens the CHECK, to allow for repeated calls, by
remembering which profiles were previously deleted during this browser
run.

(An alternative solution would be preventing duplicate profile deletions
from being triggered in the first place. But that would be slightly more
complicated, and since duplicate deletions are otherwise harmless, IMO
not worth it.)

Bug: 412932271
Change-Id: Icfe13972ce989c377c76680153d81cc071c5a777
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6519386
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1458876}