all: Remove usage of deprecated io/ioutil (#7971)

As of Go 1.16 io/ioutil is deprecated. This replaces usage with the
corresponding functions in package os and package io.

script/prune_mocks.go

@@ -12,7 +12,6 @@ package main
 import (
 	"bufio"
 	"flag"
-	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
@@ -51,7 +50,7 @@ func pruneInterfaceCheck(path string, size int64) error {
 	}
 	defer fd.Close()
 
-	tmp, err := ioutil.TempFile(".", "")
+	tmp, err := os.CreateTemp(".", "")
 	if err != nil {
 		return err
 	}