net: remove internal support for obsolete DNS record types

There are no real world use cases for HINFO, MINFO, MB, MG, or MR
records, and package net's exposed APIs don't provide any way to
access them even if there were. If a use ever does show up, we can
revive them. In the mean time, this is just effectively-dead code that
sticks around because of rr_mk.

Change-Id: I6c188b5ee32f3b3a04588b79a0ee9c2e3e725ccc
Reviewed-on: https://go-review.googlesource.com/22593
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/dnsmsg.go

@@ -163,73 +163,6 @@ func (rr *dnsRR_CNAME) Walk(f func(v interface{}, name, tag string) bool) bool {
 	return rr.Hdr.Walk(f) && f(&rr.Cname, "Cname", "domain")
 }
 
-type dnsRR_HINFO struct {
-	Hdr dnsRR_Header
-	Cpu string
-	Os  string
-}
-
-func (rr *dnsRR_HINFO) Header() *dnsRR_Header {
-	return &rr.Hdr
-}
-
-func (rr *dnsRR_HINFO) Walk(f func(v interface{}, name, tag string) bool) bool {
-	return rr.Hdr.Walk(f) && f(&rr.Cpu, "Cpu", "") && f(&rr.Os, "Os", "")
-}
-
-type dnsRR_MB struct {
-	Hdr dnsRR_Header
-	Mb  string `net:"domain-name"`
-}
-
-func (rr *dnsRR_MB) Header() *dnsRR_Header {
-	return &rr.Hdr
-}
-
-func (rr *dnsRR_MB) Walk(f func(v interface{}, name, tag string) bool) bool {
-	return rr.Hdr.Walk(f) && f(&rr.Mb, "Mb", "domain")
-}
-
-type dnsRR_MG struct {
-	Hdr dnsRR_Header
-	Mg  string `net:"domain-name"`
-}
-
-func (rr *dnsRR_MG) Header() *dnsRR_Header {
-	return &rr.Hdr
-}
-
-func (rr *dnsRR_MG) Walk(f func(v interface{}, name, tag string) bool) bool {
-	return rr.Hdr.Walk(f) && f(&rr.Mg, "Mg", "domain")
-}
-
-type dnsRR_MINFO struct {
-	Hdr   dnsRR_Header
-	Rmail string `net:"domain-name"`
-	Email string `net:"domain-name"`
-}
-
-func (rr *dnsRR_MINFO) Header() *dnsRR_Header {
-	return &rr.Hdr
-}
-
-func (rr *dnsRR_MINFO) Walk(f func(v interface{}, name, tag string) bool) bool {
-	return rr.Hdr.Walk(f) && f(&rr.Rmail, "Rmail", "domain") && f(&rr.Email, "Email", "domain")
-}
-
-type dnsRR_MR struct {
-	Hdr dnsRR_Header
-	Mr  string `net:"domain-name"`
-}
-
-func (rr *dnsRR_MR) Header() *dnsRR_Header {
-	return &rr.Hdr
-}
-
-func (rr *dnsRR_MR) Walk(f func(v interface{}, name, tag string) bool) bool {
-	return rr.Hdr.Walk(f) && f(&rr.Mr, "Mr", "domain")
-}
-
 type dnsRR_MX struct {
 	Hdr  dnsRR_Header
 	Pref uint16
@@ -382,11 +315,6 @@ func (rr *dnsRR_AAAA) Walk(f func(v interface{}, name, tag string) bool) bool {
 // Map of constructors for each RR wire type.
 var rr_mk = map[int]func() dnsRR{
 	dnsTypeCNAME: func() dnsRR { return new(dnsRR_CNAME) },
-	dnsTypeHINFO: func() dnsRR { return new(dnsRR_HINFO) },
-	dnsTypeMB:    func() dnsRR { return new(dnsRR_MB) },
-	dnsTypeMG:    func() dnsRR { return new(dnsRR_MG) },
-	dnsTypeMINFO: func() dnsRR { return new(dnsRR_MINFO) },
-	dnsTypeMR:    func() dnsRR { return new(dnsRR_MR) },
 	dnsTypeMX:    func() dnsRR { return new(dnsRR_MX) },
 	dnsTypeNS:    func() dnsRR { return new(dnsRR_NS) },
 	dnsTypePTR:   func() dnsRR { return new(dnsRR_PTR) },