demo_mode: Send clean up request with last device id

Persist sign in scope device id as session id to local state and send
with clean up request in next session. This device id cannot be used to
set up demo account for a second time. It will be used as a session
identifier on server side.

Bug: 370808139
Change-Id: I10d6a0995f7796eea287481cc0630b2eefeff6ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5967676
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Li Lin <llin@chromium.org>
Commit-Queue: Xiqi Ruan <xiqiruan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1385398}