Confirm that Briar Desktop is shutting down like Android

Briar Android's shutdown is handled in BriarService::onDestroy

https://code.briarproject.org/briar/briar/-/blob/a53a49e543e3190f329b8608ecec157da4047b89/briar-android/src/main/java/org/briarproject/briar/android/BriarService.java#L206

and BriaService::shutdownFromBackground

https://code.briarproject.org/briar/briar/-/blob/a53a49e543e3190f329b8608ecec157da4047b89/briar-android/src/main/java/org/briarproject/briar/android/BriarService.java#L264

There, there are some more Android specific stuff like wakelocks, stopForeground() and unregisterReceiver() calls, but in general it does the same like Desktop: call stopServices() and then waitForShutdown().

As part of this TODO search, I created the following issues and comments between those two chat logs:

• https://chat.briarproject.org/briar/pl/xq3oewf8q7b7mmzryp7dsimawy
• https://chat.briarproject.org/briar/pl/axa877burpypufhmkb8r4k8m6a

Besides this single TODO I found no other TODO comment either important enough to create a new issue or comment or eligible to get removed.

Fixes #140 (closed)

Closes #140 (closed)