Remove the BIP61 REJECT code from error messages and logs when a
transaction is rejected.
BIP61 support was removed from Bitcoin Core in
fa25f43ac5. The REJECT codes will be
removed from the codebase entirely in the following commit.
Adds the following util units and adds them to libbitcoin_util:
- `util/url.cpp` takes `urlDecode` from `httpserver.cpp`
- `util/error.cpp` takes `TransactionErrorString` from
`node/transaction.cpp` and `AmountHighWarn` and `AmountErrMsg` from
`ui_interface.cpp`
- `util/fees.cpp` takes `StringForFeeReason` and `FeeModeFromString` from `policy/fees.cpp`
- `util/rbf.cpp` takes `SignalsOptInRBF` from `policy/rbf.cpp`
- 'util/validation.cpp` takes `FormatStateMessage` and `strMessageMagic` from 'validation.cpp`
