simapp InitChainer: use json instead of tmjson (#7523)

* simapp InitChainer: use json instead of tmjson

* First run for test

* Revert export_test

Co-authored-by: Alessio Treglia <alessio@tendermint.com>

simapp/app.go

@@ -1,6 +1,7 @@
 package simapp
 
 import (
+	"encoding/json"
 	"io"
 	"net/http"
 	"os"
@@ -10,7 +11,6 @@ import (
 	"github.com/rakyll/statik/fs"
 	"github.com/spf13/cast"
 	abci "github.com/tendermint/tendermint/abci/types"
-	tmjson "github.com/tendermint/tendermint/libs/json"
 	"github.com/tendermint/tendermint/libs/log"
 	tmos "github.com/tendermint/tendermint/libs/os"
 	tmproto "github.com/tendermint/tendermint/proto/tendermint/types"
@@ -484,7 +484,7 @@ func (app *SimApp) EndBlocker(ctx sdk.Context, req abci.RequestEndBlock) abci.Re
 // InitChainer application update at chain initialization
 func (app *SimApp) InitChainer(ctx sdk.Context, req abci.RequestInitChain) abci.ResponseInitChain {
 	var genesisState GenesisState
-	if err := tmjson.Unmarshal(req.AppStateBytes, &genesisState); err != nil {
+	if err := json.Unmarshal(req.AppStateBytes, &genesisState); err != nil {
 		panic(err)
 	}
 	return app.mm.InitGenesis(ctx, app.appCodec, genesisState)