Remove deprecated method. (#2481)

testing/random.go

@@ -5,17 +5,17 @@ import (
 	"time"
 )
 
-func init() {
-	rand.Seed(time.Now().UnixNano())
-}
-
 const letterBytes = "abcdefghijklmnopqrstuvwxyz"
 
+var (
+	random = rand.New(rand.NewSource(time.Now().UnixNano()))
+)
+
 // Copied from https://stackoverflow.com/a/31832326 with thanks
 func RandStringBytesRmndr(n int) string {
 	b := make([]byte, n)
 	for i := range b {
-		b[i] = letterBytes[rand.Int63()%int64(len(letterBytes))]
+		b[i] = letterBytes[random.Int63()%int64(len(letterBytes))]
 	}
 	return string(b)
 }