[Bug] Elements-23.2.2 with CT discount cannot send full balance less fee

When `sendtoaddress` is called to send the whole liquid balance less margin for fee (75-200 sats) CT discount is not applied and results in:
```
error code: -6
error message:
Insufficient funds
```

https://github.com/ElementsProject/peerswap/pull/304#issuecomment-2303931071

We understand there is an option `subtractfeefromamount`, but prefer not to use it.