Settings: make FRP wipe dialog not cancelable

User should not be able to interact with the screen after the process
has started. Otherwise we can get in a bad state and never perform the
factory reset.

Ref: CYNGNOS-427
Change-Id: I197a6ca70487a33b0ce402fda7a2d58828e8e1bb
Signed-off-by: Roman Birg <roman@cyngn.com>
(cherry picked from commit 1f6f2874)