Speculative fix of crash in TabletModeController

From the crash stack, it looks like that it might be possible that
TabletModeController was not removed itself as an observer of
ui::DeviceDataManager successfully when the system is suspended, which
might cause a crash from TabletModeController being added as an observer
twice after the system suspend is done.

Bug: b/271634754
Change-Id: I66dc8ef5e1d3b2b9c238b0a75959011f02e4d727
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4326944


Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118916}