Revert "device/fido/mac: encrypt credential metadata in the macOS keychain"

This reverts commit 7acb4716808f303c7c8bafc762f1fcda769a33bd.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 564609 as the
culprit for failures in the build cycles as shown on:
https://findit-for-me.appspot.com/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtLzdhY2I0NzE2ODA4ZjMwM2M3YzhiYWZjNzYyZjFmY2RhNzY5YTMzYmQM

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.mac/Mac10.11%20Tests/27041

Sample Failed Step: device_unittests on Mac-10.11

Original change's description:
> device/fido/mac: encrypt credential metadata in the macOS keychain
> 
> This adds a CredentialMetadata class to encrypt any account metadata
> associated with a WebAuthn credential (user ID, user name, user display
> name, and RP ID) before writing it to the macOS keychain.
> 
> The key will be generated and stored in the Chrome profile under which
> the credential was created. (It is currently hardcoded but I'm changing
> that in a follow-up CL.) Deletion of the profile or key will therefore
> render the data unreadable.
> 
> Bug: 678128
> Change-Id: I536d537e9220cc5f89d487c7f94e169d06d62e7a
> Reviewed-on: https://chromium-review.googlesource.com/1073708
> Reviewed-by: Balazs Engedy <engedy@chromium.org>
> Reviewed-by: Adam Langley <agl@chromium.org>
> Commit-Queue: Martin Kreichgauer <martinkr@google.com>
> Cr-Commit-Position: refs/heads/master@{#564609}

Change-Id: I24c8937ae0855ce542e16f0fa9f21ca159d51abe
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 678128
Reviewed-on: https://chromium-review.googlesource.com/1087613
Cr-Commit-Position: refs/heads/master@{#564659}
12 files changed