Drop Cosmos SDK 0.42 support

[webmaster128]

Cosmos SDK 0.42 reached end of life:

[webmaster128]

With this we should use tx_bytes in the simulate query:

// SimulateRequest is the request type for the Service.Simulate
// RPC method.
message SimulateRequest {
  // tx is the transaction to simulate.
  // Deprecated. Send raw tx bytes instead.
  cosmos.tx.v1beta1.Tx tx = 1 [deprecated = true];
  // tx_bytes is the raw transaction.
  //
  // Since: cosmos-sdk 0.43
  bytes tx_bytes = 2;
}