* Add WeightToFee and LengthToFee impls to RPC

* Remove RPC additions

* Update frame/transaction-payment/rpc/runtime-api/src/lib.rs

Co-authored-by: joe petrowski <[email protected]>

* Add comments to length_to_fee and weight_to_fee

Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: Oliver Tale-Yazdi <[email protected]>