#565 Delete an existing program assessment in the database

This PR closes https://github.com/OpenTree-Education/rhizone-lms/issues/565 issue. The DELETE /curriculum/:curriculumAssessmentId route deletes an existing program assessment in the database.

DELETE /curriculum/:curriculumAssessmentId route and the service file functions were implemented.

Test coverage are done to ensure the code written for the test will behave as expected by the protocol we previously defined.

Checklist

[x] Related issue appears at beginning of pull request title with pound sign, and title describes the changes being proposed.
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