cmd/pprof: remove redundant URLs from error messages in fetch.FetchURL

Errors from http.Client already includes the URL in the message.

Fixes #18754

Change-Id: I65fc25a8f3aa6a2d4627aac3fb47eed8d3c4151a
Reviewed-on: https://go-review.googlesource.com/35650Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/pprof/internal/fetch/fetch.go

@@ -49,7 +49,7 @@ func Fetcher(source string, timeout time.Duration, ui plugin.UI) (*profile.Profi
 func FetchURL(source string, timeout time.Duration) (io.ReadCloser, error) {
 	resp, err := httpGet(source, timeout)
 	if err != nil {
-		return nil, fmt.Errorf("http fetch %s: %v", source, err)
+		return nil, fmt.Errorf("http fetch: %v", err)
 	}
 	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("server response: %s", resp.Status)