[ios] Removes BVC dependencies from external_file_remover.

This is CL 1 of 2 for removing BrowsingDataRemovalControllerDelegate.

Bug: 648940
Change-Id: I18d43e008388138d303ad165a313110d2c3b940c
Reviewed-on: https://chromium-review.googlesource.com/654377
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501630}
4 files changed