gitindex: remove fetch.origin setting, which breaks with git 2.21

Fixes #81

Change-Id: I1f3e376097d889d57987f4a790c2720bf452b1f8
diff --git a/gitindex/clone.go b/gitindex/clone.go
index a957964..9851e88 100644
--- a/gitindex/clone.go
+++ b/gitindex/clone.go
@@ -53,8 +53,7 @@
 
 	cmd := exec.Command(
 		"git", "clone", "--bare", "--verbose", "--progress",
-		// Only fetch branch heads, and ignore note branches.
-		"--config", "remote.origin.fetch=+refs/heads/*:refs/heads/*")
+	)
 	cmd.Args = append(cmd.Args, config...)
 	cmd.Args = append(cmd.Args, cloneURL, repoDest)
 
@@ -64,5 +63,6 @@
 	if err := cmd.Run(); err != nil {
 		return "", err
 	}
+
 	return repoDest, nil
 }