pytest: fix psbt db test.

When we rewrite, we actually use the remote channel_announcement signatures from the db, and notice that l1 here is actually l2:

```
0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#1: gossipd rejected our channel announcement: WARNING: Bad node_signature_1 304402204ad9f0ca9b5f1f8eec61290b6008bf2c15f011e35543d25c35c5b89d2e1a183402201aaca5883714dbe11d6ae00a146fac7302352e1b9e987eee5ce98e8eb6a82909 hash e713698e14d3d8f973210e8d93c96d1a7c117c58340ccb195785a672fd0b5ef1 on channel_announcement 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
```

Explicitly remove those messages.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/test_db.py

@@ -215,6 +215,12 @@ def test_last_tx_psbt_upgrade(node_factory, bitcoind):
 
     bitcoind.rpc.decoderawtransaction(last_txs[1].hex())
 
+    # FIXME: gossipd gets upset, since it seems like the db with remote announcement_sigs was
+    # actually from l2, not l1.  But if we make this l1, then last_tx changes, so we just
+    # filter out gossipd messages here (we will still detect other broken msgs!)
+    l1.daemon.logs = [l for l in l1.daemon.logs if 'gossipd' not in l]
+    l2.daemon.logs = [l for l in l2.daemon.logs if 'gossipd' not in l]
+
 
 @pytest.mark.slow_test
 @unittest.skipIf(os.getenv('TEST_DB_PROVIDER', 'sqlite3') != 'sqlite3', "This test is based on a sqlite3 snapshot")