Filter LegacyWaitForFundingConfirmed on startup (#549)

There are two reasons why a channel would be in this state:
a) The peer was shut down during channel creation. The funding tx got
published but the peer hasn't been started since.
b) The channel creation was actually aborted, and not only will the
funding tx never be published, the channel was forgotten altogether by
the counterparty. In this case, the channel stays permanently in the
state `Syncing(LegacyWaitForFundingConfirmed)` because the counterparty
never sends `channel_reestablish` and lightning-kmp will not send his
when the remote backup is enabled.

There are some users in the b) case, it caused them to be stuck during
migration (because we were checking that all states were either synced
or closed). We published a path, but then the same users are stuck with
the swap-in, because we do the same kind of check.

I fail to see why we even stored channels in that state in the first
place: either the channel was actually created and it would be restored
upon reconnection, or the channel creation was aborted and it's better
to forget about it.

src/commonMain/kotlin/fr/acinq/lightning/io/Peer.kt

@@ -225,7 +225,7 @@ class Peer(
         }
         launch {
             // we don't restore closed channels
-            val bootChannels = db.channels.listLocalChannels().filterNot { it is Closed }
+            val bootChannels = db.channels.listLocalChannels().filterNot { it is Closed || it is LegacyWaitForFundingConfirmed }
             _bootChannelsFlow.value = bootChannels.associateBy { it.channelId }
             val channelIds = bootChannels.map {
                 logger.info { "restoring channel ${it.channelId} from local storage" }