[iOS] Add flag for system capabilities in HistorySyncCapabilitiesFetcher

_authenticationService->GetPrimaryIdentity (L130) is crashing on M124
but not on M125. This CL allows switching off using system identity
for the History Sync capability fetcher.

Bug: 330495812
Change-Id: I9de07070e1f947705b65abf168511c7f60e6ce1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401781


Reviewed-by: Nohemi Fernandez <fernandex@chromium.org>
Commit-Queue: Duong Dac <ddac@chromium.org>
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280269}