Remove dnsutil.Dedup (#1867)

Remove the code and remove the call in etcd and kubernetes handlers.
This does mean we should not add dups in the first place, which means
adding maps in backend_lookup to prevent dups from begin added.

This should cut down on the allocations because dnsutil.Dedup is very
expensive by converting everything to strings, we avoid doing that now.

plugin/etcd/msg/service.go

@@ -2,7 +2,6 @@
 package msg
 
 import (
-	"fmt"
 	"net"
 	"strings"
 
@@ -37,36 +36,6 @@ type Service struct {
 	Key string `json:"-"`
 }
 
-// RR returns an RR representation of s. It is in a condensed form to minimize space
-// when this is returned in a DNS message.
-// The RR will look like:
-//	1.rails.production.east.skydns.local. 300 CH TXT "service1.example.com:8080(10,0,,false)[0,]"
-//                      etcd Key              Ttl               Host:Port          <   see below   >
-// between parens: (Priority, Weight, Text (only first 200 bytes!), Mail)
-// between blockquotes: [TargetStrip,Group]
-// If the record is synthesised by CoreDNS (i.e. no lookup in etcd happened):
-//
-//	TODO(miek): what to put here?
-//
-func (s *Service) RR() *dns.TXT {
-	l := len(s.Text)
-	if l > 200 {
-		l = 200
-	}
-	t := new(dns.TXT)
-	t.Hdr.Class = dns.ClassCHAOS
-	t.Hdr.Ttl = s.TTL
-	t.Hdr.Rrtype = dns.TypeTXT
-	t.Hdr.Name = Domain(s.Key)
-
-	t.Txt = make([]string, 1)
-	t.Txt[0] = fmt.Sprintf("%s:%d(%d,%d,%s,%t)[%d,%s]",
-		s.Host, s.Port,
-		s.Priority, s.Weight, s.Text[:l], s.Mail,
-		s.TargetStrip, s.Group)
-	return t
-}
-
 // NewSRV returns a new SRV record based on the Service.
 func (s *Service) NewSRV(name string, weight uint16) *dns.SRV {
 	host := targetStrip(dns.Fqdn(s.Host), s.TargetStrip)