Update InstrumentContext spec to use SurveyTaker.  #3500.

This commit also brings reference identifiers in associated test
surveys into sync with what's in the actual instruments.
Remove SurveyCompletion for Contact spec.  #3500.

It's not used.
Update Participant spec to use SurveyTaker.  #3500.
Update SampledPersonsIneligibility spec to use SurveyTaker.  #3500.