[management] remove old math rand lib (#6836)

management/server/util/util.go

@@ -1,5 +1,20 @@
 package util
 
+import (
+	"crypto/rand"
+	"math/big"
+)
+
+// RandIntn returns a uniformly distributed int in [0, n) sourced from
+// crypto/rand. It panics if n <= 0 or the platform randomness source fails.
+func RandIntn(n int) int {
+	v, err := rand.Int(rand.Reader, big.NewInt(int64(n)))
+	if err != nil {
+		panic(err)
+	}
+	return int(v.Int64())
+}
+
 // Difference returns the elements in `a` that aren't in `b`.
 func Difference(a, b []string) []string {
 	mb := make(map[string]struct{}, len(b))