[ios] Avoid automatic service creation during tests

If the KeyedService are created automatically with the profile, then it
should not be created during unit tests otherwise it is not possible to
use a TestProfileIOS without this service (and then the tests cannot be
independent from the service).

To prevent this add an assertion in ProfileKeyedServiceFactoryIOS (and
the refcounted variant) that only one of the two flags is set and update
the unit tests accordingly.

Bug: none
Change-Id: I10a0ac1ff39cc3489983532ad0410fac586a9a19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6494790
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Louis Romero <lpromero@google.com>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1456245}