Default CDMA subscription source to RUIM/SIM

Operators read CDMA subscription from RUIM/SIM now thus change
the default hardcoded preference everywhere. Add code clean-up to
make the default come from a single source, the Phone interface.

Additional rework proposed in http://b/62299272, but this corrects
immediate issue where CDMA SSM was defaulting to NV instead of RUIM
/SIM and caused CSIM subscription to not load and 'no sim' symptom
for many users.

Bug: 62143087
Test: None
Change-Id: I32b1f1e40c736a566df824218a6565de851ce161