eth: remove disused peer_util.go

eth/peer_util.go

-package eth
-
-import (
-	"encoding/json"
-
-	"github.com/ethereum/go-ethereum/common"
-)
-
-func WritePeers(path string, addresses []string) {
-	if len(addresses) > 0 {
-		data, _ := json.MarshalIndent(addresses, "", "    ")
-		common.WriteFile(path, data)
-	}
-}
-
-func ReadPeers(path string) (ips []string, err error) {
-	var data string
-	data, err = common.ReadAllFile(path)
-	if err != nil {
-		json.Unmarshal([]byte(data), &ips)
-	}
-	return
-}