message: proto-signing: Use OfflineAminoSigner from amino
diff: -import { StdSignature } from "@cosmjs/amino";
  -import { OfflineSigner as OfflineAminoSigner } from "@cosmjs/launchpad";
  +import { OfflineAminoSigner, StdSignature } from "@cosmjs/amino";
  import { SignDoc } from "./codec/cosmos/tx/v1beta1/tx";
  