spec: delete incorrect obsolete mention of selector working on pointer to interface type.
spec: delete incorrect obsolete mention of selector working on
pointer to interface type.

R=golang-dev, niemeyer, gri
CC=golang-dev
http://codereview.appspot.com/4173067

firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang-old