net/http: Removed some unused constants in request.go.

Change-Id: I05cdf357249166a45105703e9317793aa2088844
Reviewed-on: https://go-review.googlesource.com/5560Reviewed-by: Andrew Gerrand <adg@golang.org>

src/net/http/request.go

@@ -25,9 +25,6 @@ import (
 )
 
 const (
-	maxValueLength   = 4096
-	maxHeaderLines   = 1024
-	chunkSize        = 4 << 10  // 4 KB chunks
 	defaultMaxMemory = 32 << 20 // 32 MB
 )