http: cleaned up HEAD request method.

Removed a redefinition of the request URL which is never used and
redundant checking of the return value from send().

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/4184061

src/pkg/http/client.go

@@ -321,11 +321,7 @@ func Head(url string) (r *Response, err os.Error) {
 	if req.URL, err = ParseURL(url); err != nil {
 		return
 	}
-	url = req.URL.String()
-	if r, err = send(&req); err != nil {
-		return
-	}
-	return
+	return send(&req)
 }
 
 type nopCloser struct {