refactor: move from io/ioutil to io and os package (#17109)

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

routers/web/repo/wiki_test.go

@@ -5,7 +5,7 @@
 package repo
 
 import (
-	"io/ioutil"
+	"io"
 	"net/http"
 	"testing"
 
@@ -47,7 +47,7 @@ func wikiContent(t *testing.T, repo *models.Repository, wikiName string) string
 	reader, err := entry.Blob().DataAsync()
 	assert.NoError(t, err)
 	defer reader.Close()
-	bytes, err := ioutil.ReadAll(reader)
+	bytes, err := io.ReadAll(reader)
 	assert.NoError(t, err)
 	return string(bytes)
 }