Remove largely useless checks in chanmon_consistency fuzzer

Remove largely useless checks in chanmon_consistency fuzzer

When reloading nodes A or C, the chanmon_consistency fuzzer
currently calls `get_and_clear_pending_msg_events` on the node,
potentially causing additional `ChannelMonitor` or `ChannelManager`
updates, just to check that no unexpected messages are generated.

There's not much reason to do so, the fuzzer could always swap for
a different command to call the same method, and the additional
checking requires some weird monitor persistence introspection.

Here we simplify the fuzzer by simply removing this logic.