net/http: remove unnecessary slicing

Change-Id: Ie7248c9e7f60c121e6137f28803c8fa2709f2d92
Reviewed-on: https://go-review.googlesource.com/c/net/+/444395
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
diff --git a/http2/transport.go b/http2/transport.go
index c5d005b..5f1d462 100644
--- a/http2/transport.go
+++ b/http2/transport.go
@@ -1612,7 +1612,7 @@
 
 	var sawEOF bool
 	for !sawEOF {
-		n, err := body.Read(buf[:len(buf)])
+		n, err := body.Read(buf)
 		if hasContentLen {
 			remainLen -= int64(n)
 			if remainLen == 0 && err == nil {