Sync cleanup: Remove handling/wiring for implicit passphrase

Follow-up to https://crrev.com/c/1280268: Setting an implicit passphrase
has not been supported for a long time. This CL removes a bunch of code
to handle that case, and removes the accompanying tests.

Bug: 865936
Change-Id: I3a7ff70b06ebebde8a684dfa5343b3dba563099b
Reviewed-on: https://chromium-review.googlesource.com/c/1280724
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599894}
18 files changed