Cros Reporting: Add RemoveUserReason to RemoveUser

This change adds the ablity to pass the reason for a user being removed.
This involves adding a parameter to the remove user function of
user_manager and it's derived classes.

Bug: b:190805740
Change-Id: I297cfed9c89b17f94464f4e428c0687cf3b6cfd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3105167


Commit-Queue: Tyler Garrett <tylergarrett@chromium.org>
Reviewed-by: Leonid Baraz <lbaraz@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/main@{#919284}