Remove deprecated GetTssAddress related code in crosschain

[lumtis]

For upgrade testing: #1538
In order to run the E2E tests on V11 and test upgrade V11 -> V12. GetTssAddress moved to observer module has been reimplemented in the crosschain module to maintain compatibility with the generated client.

  // GetTssAddress queries the tss address of the module.
  // Deprecated: Moved to observer
  // TODO: remove after v12 once upgrade testing is no longer needed with v11
  rpc GetTssAddress(QueryGetTssAddressRequest) returns (QueryGetTssAddressResponse) {
    option (google.api.http).get = "/zeta-chain/crosschain/get_tss_address";
  }

Once V12 is completed, upgrade testing v11 -> v12 will no longer be necessary and compatibility will no longer be necessary. The code above should be removed.

To list the code to be removed the following line can be searched in the code

// https://github.com/zeta-chain/node/issues/1547