cmd/go: for go get -insecure, do not fall back to HTTP for non-200 responses

Since we allow non-200 responses from HTTPS in normal operation,
it seems odd to reject them in -insecure operation.

Fixes #13037 (again).

Change-Id: Ie232f7544ab192addfad407525888db6b967befe
Reviewed-on: https://go-review.googlesource.com/17945Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/http.go

@@ -83,14 +83,11 @@ func httpsOrHTTP(importPath string, security securityMode) (urlStr string, body
 		}
 	}
 	urlStr, res, err := fetch("https")
-	if err != nil || res.StatusCode != 200 {
-		if buildV && err != nil {
+	if err != nil {
+		if buildV {
 			log.Printf("https fetch failed: %v", err)
 		}
 		if security == insecure {
-			if buildV && res.StatusCode != 200 {
-				log.Printf("https fetch: status %s", res.Status)
-			}
 			closeBody(res)
 			urlStr, res, err = fetch("http")
 		}