broadband-modem: set auto registration with AT+COPS=0

This is, remove the use of "AT+COPS=0,,". The extra commas break its use in a
Nokia C7, and the proper/clean way to do it anyway is to avoid using the commas.

src/mm-broadband-modem.c

@@ -2284,7 +2284,9 @@ register_in_network (MMIfaceModem3gpp *self,
      */
     else if (REG_IS_IDLE (broadband->priv->modem_3gpp_registration_state) ||
              broadband->priv->manual_reg) {
-        command = g_strdup ("+COPS=0,,");
+        /* Note that '+COPS=0,,' (same but with commas) won't work in some Nokia
+         * phones */
+        command = g_strdup ("+COPS=0");
         broadband->priv->manual_reg = FALSE;
     }