Drop dup PeerManager tiemr_tick_occurred calls from NioPeerHandler

Drop dup PeerManager tiemr_tick_occurred calls from NioPeerHandler

We call PeerManager's timer_tick_occurred in the
lightning-background-processor crate, initialized from the
ChannelManagerConstructor. Prior to the use of the
lightning-background-processor we'd needed to call PeerManager's
timer_tick_occurred from NioPeerHandler, but we never dropped it
after the switch. Thus, every ~30 seconds we'll call
PeerManager::timer_tick_occurred twice in a row, disconnecting all
of our peers.