Remove builds conditional on go1.7 since that is now guaranteed #2154

Old fallback code was deleted and the go1.7 style code inlined where
appropriate.

backend/http/http.go

@@ -2,9 +2,6 @@
 //
 // It treats HTML pages served from the endpoint as directory
 // listings, and includes any links found as files.
-
-// +build go1.7
-
 package http
 
 import (