signond: explicitly destroy P2P socket on signond dtor
signond: explicitly destroy P2P socket on signond dtor

Destroy the P2P socket as soon as the SignonDaemon destructor is
invoked; to limit the risk of a client connecting to it while we have
already decided that we are quitting.
The client needs to handle that situation anyway, but we want to make it
less likely.

plotters/accounts-sso.signond,plotters/accounts-sso.signond,plotters/accounts-sso.signond