fa9b60c842 Remove unused TransactionError constants (MarcoFalke)
Pull request description:
Fixup to #14978, which introduced a bunch of unused enum values, such as `UNKNOWN_ERROR`, `ERROR_COUNT` and `TRANSACTION_ERR_LAST`. None of those have a meaning in the context of an `enum class`, where the compiler can infer if all cases have been covered in a switch-case.
Also, move the global `::maxTxFee` back to the rpc caller, so it can be set on a per call basis (in the future).
Tree-SHA512: 7f1e2d795f1c1278ecd54ddab2b92c2a862f3c637b482d1d008208925befa1c9dd4b3c4bb1bfcbc5ca4b66a41004aaf01ea96ea95236f944250b8a6cf99ff173
