i18n: transport-helper.c: change N_() call to _()

The N_() no-op call currently marks the string to be extracted by
xgettext but doesn't trigger the retrieval of the translation at run
time, whereas _() does both. Meaning that, in spite of having
translations available, they were never retrieved to make use of them.

Signed-off-by: Vasco Almeida <vascomalmeida@sapo.pt>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport-helper.c

@@ -1038,7 +1038,7 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 				(*tail)->status |= REF_STATUS_UPTODATE;
 				if (read_ref((*tail)->name,
 					     (*tail)->old_oid.hash) < 0)
-					die(N_("Could not read ref %s"),
+					die(_("Could not read ref %s"),
 					    (*tail)->name);
 			}
 		}