[sat] use new ntn signal strength TelephonyCallback

This can replace the current method of calculating the signal strength
for a carrier NTN connection.

Test: MobileIconInteractorTest
Bug: 377518113
Flag: com.android.internal.telephony.flags.carrier_roaming_nb_iot_ntn
Change-Id: Id64d90a8e55de3ac5f0c72d78ccfe2664c83a93a