cmd/golangorg: change tab width from 8 to 4 in production

Remove the override, use the default godoc.Presentation value of 4.
This increases consistency across various Go websites, and reduces
the amount of blank horizontal space use.

Fixes golang/go#34448

Change-Id: Ie3e40f13e6275e74e79c46bbc242d4e5ad95ffda
Reviewed-on: https://go-review.googlesource.com/c/website/+/196937
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>

cmd/golangorg/appinit.go

@@ -101,7 +101,6 @@ func main() {
 	}
 
 	pres = godoc.NewPresentation(corpus)
-	pres.TabWidth = 8
 	pres.ShowPlayground = true
 	pres.DeclLinks = true
 	pres.NotesRx = regexp.MustCompile("BUG")