Correct Print Backend service timeout handling

Fix the idle handler for the Print Backend service, which has been
incorrectly using a hardcoded value.

Improve one of the logging lines to provide extra detail of client type
which is being unregistered.

Fixed: 1431997
Change-Id: I673c8956e57d5333e948d99f891a99483b62a8ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4426167
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Alan Screen <awscreen@chromium.org>
Reviewed-by: Andy Phan <andyphan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1130677}