signond: on idle timeout, directly delete all AuthSessions
signond: on idle timeout, directly delete all AuthSessions

This reverts commit 2f4f9dabce683abab493c8db34a29f5439b71e77 which had
just this explanation as message: "resolving crash, happened during
qDeleteAll() calling", without explaining why the substituted code was
causing a crash (this was more than three years ago).
Deleting the AuthSession before re-entering the main loop (which is what
would happen with just deleteLater()) is important because this causes
the objects to be unregistered from their D-Bus connection(s).
Otherwise, there's a tiny time window in which the AuthSession is still
present on the bus, accepting method calls, but then being silently
deleted almost immediately.
For some reason, the Ubuntu builder seems very clever in reproducing
this scenario:
https://launchpadlibrarian.net/156787606/buildlog_ubuntu-trusty-amd64.signon_8.55bzr604trusty0_FAILEDTOBUILD.txt.gz

We could obtain the same result by simply emitting the destroyed()
signal from the AuthSession objects (note: *not* from their parent
SignonSessionCore itself -- as this code was doing -- because that's not
registered in any D-Bus connection). However, there doesn't seem a
reason to delay the destruction of the AuthSessions.


Distrotech/signon,Distrotech/signon,Distrotech/signon