iface-modem-messaging: automatically detect the best default storage

Instead of letting the plugins specify a default storage to use, just look at
the supported ones and use the best one.

"MT is preferred over "ME" or "SM", as "MT=ME+SM"

plugins/cinterion/mm-broadband-modem-cinterion.c

@@ -1163,7 +1163,6 @@ mm_broadband_modem_cinterion_new (const gchar *device,
                          MM_BASE_MODEM_PLUGIN, plugin,
                          MM_BASE_MODEM_VENDOR_ID, vendor_id,
                          MM_BASE_MODEM_PRODUCT_ID, product_id,
-                         MM_IFACE_MODEM_MESSAGING_SMS_DEFAULT_STORAGE, MM_SMS_STORAGE_MT,
                          NULL);
 }