1292 Fix sample deletion

[jacobtylerwalls]

Fixes #1292

Reverting the fix causes the added test to fail (as desired):

arches-for-science % PYTHONPATH='../arches' python3 manage.py test --settings=arches_for_science.test_settings --keepdb
Found 2 test(s).
Using existing test database for alias 'default'...
creating index : test_terms
creating index : test_concepts
creating index : test_resources
System check identified no issues (1 silenced).
.F
======================================================================
FAIL: test_create_delete_sample (arches_for_science.tests.AnalysisAreaAndSampleTakingTests)
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Traceback (most recent call last):
  File "/Users/jwalls/prj/arches-for-science/arches_for_science/tests.py", line 154, in test_create_delete_sample
    self.assertEqual(response.status_code, 200)
AssertionError: 500 != 200

----------------------------------------------------------------------
Ran 2 tests in 3.566s

[njkim]

It looks good!
Deletion works as described without an error.
The test runs ok.