Remove persisted docked windows

Disables restoring windows to a docked state if the #ash-enable-docked-windows
flag is disabled. This change was meant to be in M57 right after CL:
https://codereview.chromium.org/2617733002 had landed, but it didn't make it
before the branch point.

BUG=668355

Review-Url: https://codereview.chromium.org/2652043004
Cr-Commit-Position: refs/heads/master@{#446754}
12 files changed