Remove setIsoCountryProperty method along with partially dead code

Previously to this commit, setIsoCountryProperty method was only called
if operatorNumeric string was not empty, therefore there was no point
in verifying the opposite condition inside the method itself.

Remove the method altogether because it's private and only called in
one part of the class.

Change-Id: I76819fa84e9ace1786869f3dc32b95a150a95bde