Get rid of internal field survey_passwords

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
- API

##### SUMMARY
Since survey answers are now encrypted inside of their entry, we do not need the corresponding survey_passwords field to track which values should be redacted

##### ADDITIONAL INFORMATION

Start by searching the API implementation and schema for survey_passwords, then trace how encrypted survey answers are handled. Remove the obsolete field and confirm that survey redaction still works without it; the change is done when the API and related data model no longer depend on survey_passwords.

Written by the indexing model from the issue text.