telephony: Do not set default subscriptions on shutdown

On some devices the SIM slots are not deactivated at the same time
when the phone is shut down or rebooted. This means that at some point
only one SIM is activated, and all default subscriptions are set to
this SIM (a feature introduced in http://review.cyanogenmod.org/#/c/121239/).

Ticket: CYNGNOS-2185, CYNGNOS-2570
Change-Id: Ief36004619b75530a21b23efc767e1beb1fb0750