Remove obsolete top-level run code in tests.

tests/test_dependencies.py

@@ -37,7 +37,3 @@ class ScrapyUtilsTest(unittest.TestCase):
         pinned_twisted_version_string = match[1]
 
         self.assertEqual(twisted_version.short(), pinned_twisted_version_string)
-
-
-if __name__ == "__main__":
-    unittest.main()

tests/test_utils_iterators.py

@@ -528,7 +528,3 @@ class TestHelper(unittest.TestCase):
             type(a) is type(b), f"Got {type(a)}, expected {type(b)} for { obj!r}"
         )
         self.assertEqual(a, b)
-
-
-if __name__ == "__main__":
-    unittest.main()

tests/test_utils_python.py

@@ -258,7 +258,3 @@ class UtilsPythonTestCase(unittest.TestCase):
             without_none_values({"one": 1, "none": None, "three": 3, "four": 4}),
             {"one": 1, "three": 3, "four": 4},
         )
-
-
-if __name__ == "__main__":
-    unittest.main()