Remove synthesized CellInfo reports from ServiceStateTracker

This CL removes the legacy code from ServiceStateTracker that
was synthesizing highly incomplete CellInfo reports under very
specific conditions (only in LTE-CDMA mode). This was causing
CellInfo to be sent that consisted of a single LTE Cell Info
report that was missing information. Because this only worked
when the serving cell was LTE / the device was in LTE-CDMA mode
it was also inconsistent.

-Remove the hack to update CellInfo on unsolicited SignalStrength
 change reported by RIL (only active in LTE+CDMA mode).
-Remove the hack to update CellInfo on Data Registration State
 change.
-Remove the now-unneeded mCellInfo and mCellInfoLte structures
 from SST.
-Remove the obsolete decoding for the LTE Cell Info in the
 DATA_REGISTRATION_STATE message.

Bug: 27949013
Change-Id: I0ac6f8f93a1d1177a246d5cd2843025b8f9b34a9