go.net/ipv6: remove RawConn reference from package documentation
go.net/ipv6: remove RawConn reference from package documentation

This package doesn't have RawConn type.

R=dave
CC=golang-dev
https://golang.org/cl/10042043

gomini/net,mckinney-subgraph/net,golang/net,gomini/net,veliamsli/net,cmars/tools,subuk/net,foreversmart/net,flowlo/go-net,veliamsli/net,dafyddcrosby/net,chenzlabs/net,muzining/net,yangxianjun/net,DramaFever/golang.org-x-net,zabawaba99/net,foreversmart/net,w4ngyi/net,cmars/tools,cmars/tools,w4ngyi/net,cesanta/goxnet,kiip/net,yangxianjun/net,subuk/net,muzining/net,cmars/tools,mckinney-subgraph/net,albertjin/golang-net,DramaFever/golang.org-x-net,raboof/net,zabawaba99/net,raboof/net,cesanta/goxnet,dafyddcrosby/net,chenzlabs/net,flowlo/go-net,albertjin/golang-net,kiip/net