[1.7.x] Fixed #23651 -- Isolated non-existent fixture tests

Previous versions of the tests were buggy, as initial_data.json
did exist and the test wasn't failing. It was finally failing on
Python 3.4.2.
Thanks Raphaël Hertzog for the report (and Debian bug #765117
contributors).
Backport of 7a893ee771 from master.

tests/fixtures_regress/tests.py

@@ -16,7 +16,6 @@ from django.db.models import signals
 from django.test import (TestCase, TransactionTestCase, skipIfDBFeature,
     skipUnlessDBFeature)
 from django.test import override_settings
-from django.utils.encoding import force_text
 from django.utils._os import upath
 from django.utils import six
 from django.utils.six import PY3, StringIO
@@ -459,18 +458,6 @@ class TestFixtures(TestCase):
                 verbosity=0,
             )
 
-    def test_loaddata_not_existant_fixture_file(self):
-        stdout_output = StringIO()
-        with warnings.catch_warnings(record=True):
-            management.call_command(
-                'loaddata',
-                'this_fixture_doesnt_exist',
-                verbosity=2,
-                stdout=stdout_output,
-            )
-        self.assertTrue("No fixture 'this_fixture_doesnt_exist' in" in
-            force_text(stdout_output.getvalue()))
-
     def test_ticket_20820(self):
         """
         Regression for ticket #20820 -- loaddata on a model that inherits