cmd/releasebot: remove EDITOR=true hack in favor of --no-edit

The EDITOR env var is set to true to prevent git commit --amend
from pulling up an editor. Use the --no-edit command instead since
the desired behavior is the same only without the hack.

Change-Id: I29df9a566669ce56605169014b9e534b15811368
Reviewed-on: https://go-review.googlesource.com/83335
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cmd/releasebot/git.go

@@ -221,7 +221,7 @@ func (w *Work) cherryPickCLs() {
 			w.run("git", "cherry-pick", "--abort")
 			continue
 		}
-		w.run("git", "commit", "--amend") // commit hook puts [release-branch] prefix in
+		w.run("git", "commit", "--amend", "--no-edit") // commit hook puts [release-branch] prefix in
 
 		// Search Gerrit to find any pre-existing CL we'd be updating by doing a git mail.
 		// If one exists and it has the same parent, tree, and commit message as our local

cmd/releasebot/main.go

@@ -71,8 +71,6 @@ func main() {
 	if flag.NArg() == 0 {
 		usage()
 	}
-	// Make git editor a no-op to allow commands like "git commit --amend".
-	os.Setenv("EDITOR", "true")
 
 	http.DefaultTransport = newLogger(http.DefaultTransport)