website: remove floating topbar

This caused more problems than it was worth.

Fixes #4301.
Fixes #4317.

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/6818076

doc/style.css

@@ -519,27 +519,3 @@ div#playground .code {
 div#playground .output {
 	height: 100px;
 }
-
-/* always show topbar for large screens */
-@media screen and (min-width: 130ex) and (min-height: 300px) {
-       /* 130ex -> wide enough so that title isn't below buttons */
-
-	div#topbar.wide {
-		position: fixed;
-		z-index: 1;
-		top: 0;
-		width: 100%;
-		height: 63px;
-		border-bottom: 1px solid #B0BBC5;
-	}
-
-	div#page.wide {
-		position: fixed;
-		top: 64px; /* to match topbar */
-		bottom: 0px;
-		overflow: auto;
-		margin-left: auto;
-		margin-right: auto;
-	}
-}
-