Site data is not cleared when an output is marked as "Not applicable"

[chrisala]

To reproduce:

1. Open an NHT Output Report
2. Select a service (e.g. Flora Survey) and draw some site information for it.
3. Save the form.
4. Note the site associated with the report on the sites tab
5. Open the form again
6. Mark the service as Not applicable
7. Save the form.

Expected:
The site data from the service marked not applicable no longer shows up on the sites tab (and if that was the only data for the form, the site is removed entirely)

Actual:
The site data remains attached to the report site but is no longer referenced in the report.