Update PyXFormTestCase usages to follow default "data" form name/id

[lindsay-stevens]

As mentioned here: #712 (comment), PyXFormTestCase tests default to overriding the default form name "data" with "test_name". Some tests explicitly set the form name to "data" using the parameter name="data". These tests should all use the default name "data" implicitly, unless the test is specifically about a use case where a non-default form name is being set.