Removing hardcoded database column name

+ We were previously hardcoding the post_dial_digits column name.
This code was written before we had src-N and src-pre-N folders.
+ This CL converts the hard coded column name to follow the pattern
we have for new stuff in the SDK.
+ Additionally, this CL removes an unneeded method which checks the
SDK version, instead using the CompatUtils class.

Bug: 25021389
Change-Id: I017d47f7efd323254e616a64d7ac824c5cfb8902