chromeos: Fix comments in SessionController

We're going to keep the session_manager::SessionState to ash::LoginStatus
conversion code, so update docs to reflect that.

BUG=none
[email protected]

Review-Url: https://codereview.chromium.org/2750753002
Cr-Commit-Position: refs/heads/master@{#456572}
2 files changed