Remove dead code for migration flow

Code regarding the dialog pending view is useless now since we've
changed the design.

Previously dialog would change to a pending state with all checkboxes
and buttons disabled after the user clicks the save button. And after
5 secs a close button would show.
New design is to dismiss the dialog directly.

Bug: 852904
Change-Id: Idb0ab56f80431a8c26a6bd178ef864bcc16887f0
Reviewed-on: https://chromium-review.googlesource.com/c/1282037
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Siyu An <siyua@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599857}
4 files changed