refactor: move from io/ioutil to io and os package (#10341)

## Description

The `io/ioutil` package has been deprecated in Go 1.16 (See https://golang.org/doc/go1.16#ioutil). Since cosmos-sdk has upgraded to Go 1.17 (#9987), this PR replaces the existing `io/ioutil` functions with their new definitions in `io` and `os` packages.

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [x] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [x] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [x] reviewed "Files changed" and left comments if necessary
- [x] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

server/export.go

@@ -4,7 +4,6 @@ package server
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 
 	"github.com/spf13/cobra"
@@ -49,7 +48,7 @@ func ExportCmd(appExporter types.AppExporter, defaultNodeHome string) *cobra.Com
 					return err
 				}
 
-				genesis, err := ioutil.ReadFile(config.GenesisFile())
+				genesis, err := os.ReadFile(config.GenesisFile())
 				if err != nil {
 					return err
 				}

server/grpc/gogoreflection/serverreflection.go

@@ -41,7 +41,6 @@ import (
 	"compress/gzip"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"reflect"
 	"sort"
@@ -219,7 +218,7 @@ func decompress(b []byte) ([]byte, error) {
 	if err != nil {
 		return nil, fmt.Errorf("bad gzipped descriptor: %v", err)
 	}
-	out, err := ioutil.ReadAll(r)
+	out, err := io.ReadAll(r)
 	if err != nil {
 		return nil, fmt.Errorf("bad gzipped descriptor: %v", err)
 	}

server/grpc/grpc_web_test.go

@@ -7,7 +7,6 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/textproto"
 	"strconv"
@@ -197,7 +196,7 @@ func (s *GRPCWebTestSuite) makeGrpcRequest(
 		return nil, Trailer{}, nil, err
 	}
 	defer resp.Body.Close()
-	contents, err := ioutil.ReadAll(resp.Body)
+	contents, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, Trailer{}, nil, err
 	}

server/mock/helpers.go

@@ -2,7 +2,6 @@ package mock
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 
 	abci "github.com/tendermint/tendermint/abci/types"
@@ -14,7 +13,7 @@ import (
 func SetupApp() (abci.Application, func(), error) {
 	logger := log.NewTMLogger(log.NewSyncWriter(os.Stdout)).
 		With("module", "mock")
-	rootDir, err := ioutil.TempDir("", "mock-sdk")
+	rootDir, err := os.MkdirTemp("", "mock-sdk")
 	if err != nil {
 		return nil, nil, err
 	}