Is now intended to the used for user deinitialization.
This fixes mail_user_session_finished event not being sent
with managesieve.

It only causes confusing output.

The dump-capability just wants to get the capabilities. Any problems with
settings will be handled later on.

Also change the callers to not bother storing it separately. Instead, they
can just use mail_user_r->service_user.

Use named initializers and list the items on a separate line each.

This also drops the trailing period from the log message, which matches the
changes to core.

This enables race-free kicking using socket+SIGTERM.