[ios] Migrate ClearBrowsingDataManager to the IdentityManager

Use identity::IdentityManager::HasPrimaryAccount() instead of
SigninManagerBase::IsAuthenticated, and remove unneeded includes.

Bug: 890826
Change-Id: Iabe09231fa684e8249475ba9dcd8782d7ecd90d5
Reviewed-on: https://chromium-review.googlesource.com/c/1315969
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#605735}
1 file changed