refactor(x/auth): v2 adaptable tx instead of double decode (#15910)

testutil/sims/tx_helpers.go

@@ -67,7 +67,7 @@ func GenSignedMockTx(r *rand.Rand, txConfig client.TxConfig, msgs []sdk.Msg, fee
 		}
 
 		signBytes, err := authsign.GetSignBytesAdapter(
-			context.Background(), txConfig.TxEncoder(), txConfig.SignModeHandler(), signMode, signerData,
+			context.Background(), txConfig.SignModeHandler(), signMode, signerData,
 			tx.GetTx())
 		if err != nil {
 			panic(err)

testutil/testnet/genesis.go

@@ -143,7 +143,6 @@ func (b *GenesisBuilder) GenTx(privVal secp256k1.PrivKey, val cmttypes.GenesisVa
 	// Generate bytes to be signed.
 	bytesToSign, err := authsigning.GetSignBytesAdapter(
 		context.Background(),
-		txConf.TxEncoder(),
 		txConf.SignModeHandler(),
 		signing.SignMode_SIGN_MODE_DIRECT,
 		authsigning.SignerData{