Fix backwards compatibility of NodeMetrics reads

In commit dd55d47 we started ignoring
the legacy `latest_channel_monitor_archival_height` field of
`NodeMetrics`. However, we erroneously started reading it as
`Option<u32>`, though, given it's an optional field, it should have been
read as a plain `u32` that might or might not be present. Here we fix this error.

Author: tnull

src/lib.rs

@@ -1837,7 +1837,7 @@ impl_writeable_tlv_based!(NodeMetrics, {
 	(6, latest_rgs_snapshot_timestamp, option),
 	(8, latest_node_announcement_broadcast_timestamp, option),
 	// 10 used to be latest_channel_monitor_archival_height
-	(10, _legacy_latest_channel_monitor_archival_height, (legacy, Option<u32>, |_: &NodeMetrics| None::<Option<u32>> )),
+	(10, _legacy_latest_channel_monitor_archival_height, (legacy, u32, |_: &NodeMetrics| None::<Option<u32>> )),
 });
 
 pub(crate) fn total_anchor_channels_reserve_sats(