refactor: move from io/ioutil to io and os package

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>

weed/images/resizing_test.go

@@ -2,7 +2,6 @@ package images
 
 import (
 	"bytes"
-	"io/ioutil"
 	"os"
 	"testing"
 )
@@ -10,13 +9,13 @@ import (
 func TestResizing(t *testing.T) {
 	fname := "sample2.webp"
 
-	dat, _ := ioutil.ReadFile(fname)
+	dat, _ := os.ReadFile(fname)
 
 	resized, _, _ := Resized(".webp", bytes.NewReader(dat), 100, 30, "")
 	buf := new(bytes.Buffer)
 	buf.ReadFrom(resized)
 
-	ioutil.WriteFile("resized1.png", buf.Bytes(), 0644)
+	os.WriteFile("resized1.png", buf.Bytes(), 0644)
 
 	os.Remove("resized1.png")