fix person_dob prepopulator #4018

Prepopulator trigger was not returning false when 
Person.person_dob_date returned nil, as it should.
Further the test was wrong, where the test 
description was contradicting the test assertion.
remove stubs
Merge pull request #222 from NUBIC/bug_4018_participant_verification_dob

fix person_dob prepopulator #4018