SubscriptionController: properly detect when MSIM has 1 SIM

We cannot use sSlotIdxToSubId to determine when to turn the SIM dialog
off, because when subscription information gets reloaded (on data change
for instance), we may add one, then disable SMS prompt, then add the
other, which is incorrect. Query the total number of SIMs from the info
updater.

Ticket: CYNGNOS-2185, CYNGNOS-2570

Change-Id: Iab1225c83b508e055d8a8de55c1e21e2aa153ca5
Signed-off-by: Roman Birg <roman@cyngn.com>