Don't pause events for chainsync persistence

Don't pause events for chainsync persistence

We used to wait on ChannelMonitor persistence to avoid
duplicate payment events. But this can still happen in cases where
ChannelMonitor handed the event to ChannelManager and we did not persist
ChannelManager after event handling.
It is expected to receive payment duplicate events and clients should handle these
events in an idempotent manner. Removing this hold-up of events simplifies
the logic and makes it easier to not persist ChannelMonitors on every block connect.