godoc/analysis: remove obsolete comment.
godoc/analysis: remove obsolete comment.

The bug it refers to is now fixed, and the alternative
implementation it suggests is not an improvement.

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/151620044

sshetty10/tools,cw2018/tools,springning/tools,magiccao/tools,jdhenke/tools,cmars/tools,golang/tools,runcom/tools,dmitris/tools,dmitris/tools,cw2018/tools,maddyonline/tools,magiccao/tools,golang/tools,golang/tools,syreclabs/go-tools,cmars/tools,4ad/tools,jdhenke/tools,magiccao/tools,cw2018/tools,nicot/tools,josharian/tools,maddyonline/tools,dmitris/tools,sshetty10/tools,matryer/tools,argandas/tools,springning/tools,syreclabs/go-tools,josharian/tools,glasser/golang-tools,4ad/tools,jdhenke/tools,sshetty10/tools,syreclabs/go-tools,glasser/golang-tools,jdhenke/tools,nicot/tools,cmars/tools,cmars/tools,golang/tools,glasser/golang-tools,maddyonline/tools,runcom/tools,matryer/tools,syreclabs/go-tools,sshetty10/tools,argandas/tools,cw2018/tools,runcom/tools,nicot/tools,matryer/tools,springning/tools,4ad/tools,syreclabs/go-tools,josharian/tools,argandas/tools,josharian/tools,syreclabs/go-tools,golang/tools,glasser/golang-tools,argandas/tools,maddyonline/tools,magiccao/tools,nicot/tools,dmitris/tools,springning/tools,matryer/tools,runcom/tools