Parametrize `test_classifications`

Refs #234

It seems slower with parametrize (time tox -- tests/test_elements_worker/test_classifications.py )

With parametrize:

real	0m26,853s
user	0m9,453s
sys	0m0,800s

Without:

real	0m15,225s
user	0m5,799s
sys	0m0,414s

tests/test_elements_worker/test_classifications.py

@@ -10,6 +10,8 @@ from arkindex_worker.models import Element
 
 from . import BASE_API_CALLS
 
+# Special string used to know if the `arg_name` passed in
+# `pytest.mark.parametrize` should be removed from the payload
 DELETE_PARAMETER = "DELETE_PARAMETER"