Revert "Mash cleanup: begin converting login mojo to C++"

This reverts commit db977c4b6c6bc31bd6d601273acc921435edda83.

Reason for revert: Suspected culprit for failing Linux ChromiumOS MSan Tests. https://findit-for-me.appspot.com/waterfall/failure?url=https://build.chromium.org/p/chromium.memory/builders/Linux%20ChromiumOS%20MSan%20Tests/builds/13070

Original change's description:
> Mash cleanup: begin converting login mojo to C++
> 
> This patch moves types implemented in login_user_info.mojom to
> //ash/public/cpp/login_types.h. The handful of methods on
> mojom::LoginScreen which used these types are moved to C++
> interfaces.
> 
> There are two new public-facing C++ interfaces:
> 1. ash::LoginScreen, which is a direct translation of the mojom.
>    This is implemented by ash::LoginScreenController.
> 2. ash::LoginScreenModel, which is used for the methods that
>    were simple thunks in LoginScreenController.
>    (LoginDataDispatcher implements this interface.)
> 
> Bug: 958206
> Change-Id: I329d606b234556bf05aee40849f3aa5ccc6c0be0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610588
> Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
> Reviewed-by: Tom Sepez <tsepez@chromium.org>
> Commit-Queue: Evan Stade <estade@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#662372}

TBR=xiyuan@chromium.org,estade@chromium.org,tsepez@chromium.org

Change-Id: I0b132ea591725613e9cf2751a099f8376546a18f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 958206
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626420
Reviewed-by: Lowell Manners <lowell@chromium.org>
Commit-Queue: Lowell Manners <lowell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662577}
87 files changed