gotip: don't set User-Agent for http.DefaultTransport

This code was copied from ./internal/version in CL 206537 with the
intention of making the gotip command more consistent with the other
golang.org/dl/go... commands. However, the gotip command does not
use net/http at all, so setting a custom user agent has no effect.

Change-Id: I1632aa5f01d9c1a2541219d2649d7dc57ac259b5
Reviewed-on: https://go-review.googlesource.com/c/dl/+/207097
Reviewed-by: Bryan C. Mills <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

gotip/main.go

@@ -18,7 +18,6 @@ import (
  "errors"
  "fmt"
  "log"
- "net/http"
  "os"
  "os/exec"
  "os/user"
@@ -27,10 +26,6 @@ import (
  "strings"
 )
 
-func init() {
- http.DefaultTransport = &userAgentTransport{http.DefaultTransport}
-}
-
 func main() {
  log.SetFlags(0)
 
@@ -186,15 +181,6 @@ func homedir() (string, error) {
  }
 }
 
-type userAgentTransport struct {
- rt http.RoundTripper
-}
-
-func (uat userAgentTransport) RoundTrip(r *http.Request) (*http.Response, error) {
- r.Header.Set("User-Agent", "golang-x-build-version/devel")
- return uat.rt.RoundTrip(r)
-}
-
 // dedupEnv returns a copy of env with any duplicates removed, in favor of
 // later values.
 // Items are expected to be on the normal environment "key=value" form.