website: remove floating topbar
website: remove floating topbar

This caused more problems than it was worth.

Fixes issue 4301.
Fixes issue 4317.

R=golang-dev, minux.ma, rsc
CC=golang-dev
http://codereview.appspot.com/6818076

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