net/http: delete vestigial method

Fixes #19850

Change-Id: I8c86e288159408c687c2a85f458ade282adae450
Reviewed-on: https://go-review.googlesource.com/45077
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/request.go

@@ -1043,11 +1043,6 @@ type maxBytesReader struct {
 	err error         // sticky error
 }
 
-func (l *maxBytesReader) tooLarge() (n int, err error) {
-	l.err = errors.New("http: request body too large")
-	return 0, l.err
-}
-
 func (l *maxBytesReader) Read(p []byte) (n int, err error) {
 	if l.err != nil {
 		return 0, l.err