Standardize RTT behavior across carriers

Remove references to the ignore rtt setting carrier config key, and
treat it as always-on for all carriers.

Bug: 122250491
Bug: 130010750
Test: manual
Change-Id: I305ed17fba7910983bcd64b8221b9bba8a5d7960
Merged-In: I305ed17fba7910983bcd64b8221b9bba8a5d7960