core: remove HostAddresses() (#1728)

* core: remove HostAddresses()

config.HostAddresses() is a weird function that gathers
some data from the server and returns a string.

It is *only* used the trace plugin, to figure out what
server starts the trace.

Looks to be better to fit in the with metrics.WithServer label
on the trace itself to show which server handled the trace.

Remove HostAddresses() and cleanup trace a small bit.:w

* lint

core/dnsserver/config.go

@@ -3,7 +3,6 @@ package dnsserver
 import (
 	"crypto/tls"
 	"fmt"
-	"net"
 
 	"github.com/coredns/coredns/plugin"
 
@@ -53,22 +52,6 @@ type Config struct {
 	registry map[string]plugin.Handler
 }
 
-//HostAddresses builds a representation of the addresses of this Config
-//after server is started ONLY, can be used as a Key for identifing that config
-// :53 or 127.0.0.1:53 or 127.0.0.1:53/::1:53
-func (c *Config) HostAddresses() string {
-	all := ""
-	for _, h := range c.ListenHosts {
-		addr := net.JoinHostPort(h, c.Port)
-		if all == "" {
-			all = addr
-			continue
-		}
-		all = all + "/" + addr
-	}
-	return all
-}
-
 // keyForConfig build a key for identifying the configs during setup time
 func keyForConfig(blocIndex int, blocKeyIndex int) string {
 	return fmt.Sprintf("%d:%d", blocIndex, blocKeyIndex)