Node sends a lot of stale routing info

[sstone]

Issue and Steps to Reproduce

When connecting or reconnecting to Satoshi's place, which is running c-lightning, we receive a lot of channel ids for channels that are closed (so we query for them and check them)

getinfo output

Satoshi's place is running commit 795e0e1,

[rustyrussell]

Thanks! I found it; we keep track of recently-spent utxos (in case of reorg), but when we check if a utxo is known, we didn't check if it's actually known and spent!

This generally means if a peer sent us a channel_announcement after we'd eliminated it as dead, we restored it. Writing test now...

[cdecker]

This will be fixed by #1945