`t8ntool/transition.go:418` `unusedwrite` linter fix

We creating struct `commonTx` and then don't use it. Seems like refactoring bug from https://github.com/erigontech/erigon/pull/15413 :
```
we assign fields and then don't use them:

commonTx.V.SetFromBig(txJson.V.ToInt())
commonTx.R.SetFromBig(txJson.R.ToInt())
commonTx.S.SetFromBig(txJson.S.ToInt())
```

```
cmd/evm/internal/t8ntool/transition.go:418:8: unusedwrite: unused write to field Nonce (govet)
Nonce: uint64(txJson.Nonce),
^
cmd/evm/internal/t8ntool/transition.go:419:5: unusedwrite: unused write to field To (govet)
To: txJson.To,
^
cmd/evm/internal/t8ntool/transition.go:420:8: unusedwrite: unused write to field Value (govet)
Value: value,
^
cmd/evm/internal/t8ntool/transition.go:421:11: unusedwrite: unused write to field GasLimit (govet)
GasLimit: uint64(txJson.Gas),
^
cmd/evm/internal/t8ntool/transition.go:422:7: unusedwrite: unused write to field Data (govet)
Data: txJson.Input,
^
```