Deleting an assignment does not cleanup datapoints related entities

[iperdomo]

Context

While testing the new data point assignment functionality, we found that deleting an Assignment does not cleanup all related entities, leaving orphan data.

Problem or idea

When deleting an Assignment that contains data points assigned to a device, those entities remain even the parent object was removed.

Steps to reproduce:

• Create a new assignment that contains data points assigned to a device
• Download the datapoints to the device
• Delete the newly created assignment
• The expected behavior is that if we use the Download functionality in the device, the data point will be removed, but it remains there, because the endpoint used by the App keeps returning orphan data.

Solution or next step

• Delete the related DataPointAssignment entities when a SurveyAssignment is removed