Remove hardcoded empty option in "CountryStatesHelper::PopulateStates" method

Method "CountryStatesHelper::PopulateStates" automatically populates State dropdown with states, that match selected country (e.g. USA or Canada). However it also does 1 bad thing: adds an empty option.

As a fix I'm proposing to:

1. remove empty option addition from that method
2. check for places where states dropdown is being displayed and add has_empty="1" option there