Our "maximum fee" safety net is higher than `bitcoind`'s `maxtxfee`

[darosior]

Which can lead to unfortunate situations like:

b'[1639656110][revaultd::daemon::bitcoind::poller][WARN] Fee estimation not available, skipping CPFP'
b"[1639656110][revaultd::daemon::bitcoind::poller][DEBUG] Trying to broadcast Spend tx '35c46c8dd374b6375190c324f2185b16d10ed595e90a12bc49e5ebebe85ed8c4'"
b"[1639656110][revaultd::daemon::bitcoind::interface][DEBUG] Broadcasting '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'"
b'[1639656110][revaultd::daemon::bitcoind::poller][ERROR] Error broadcasting Spend tx \'35c46c8dd374b6375190c324f2185b16d10ed595e90a12bc49e5ebebe85ed8c4\': \'Bitcoind server error: RPC error response: RpcError { code: -25, message: "Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)", data: None }\''

I think it's still good to keep both safety nets, but opened the issue to not forget about this (again).