Add logging of user stop and user removal events.

This adds logging for user stop and remove, similar to other
user lifecycle events that are already logged, such as create
and switch.

Bug: 218688672
Test: make statsd_testdrive; statsd_testdrive <atom #>
Test: atest UserControllerTest
Change-Id: I3e16370fe0f9a2d5bddb0cfcb71a1478c8ceaaec