Remove serial test support from test-webkitpy.

Tools/Scripts/webkitpy/test/main_unittest.py

Index: Tools/Scripts/webkitpy/test/main_unittest.py
diff --git a/Tools/Scripts/webkitpy/test/main_unittest.py b/Tools/Scripts/webkitpy/test/main_unittest.py
index 0df8e5313f84aafcd1d56ac8ec2b81823ff01c79..4560d251197cde132af0322909dc5784bbad6c78 100644
--- a/Tools/Scripts/webkitpy/test/main_unittest.py
+++ b/Tools/Scripts/webkitpy/test/main_unittest.py
@@ -38,9 +38,6 @@ class TestStubs(unittest.TestCase):
     def test_empty(self):
         pass
 
-    def serial_test_empty(self):
-        pass
-
 
 class TesterTest(unittest.TestCase):
 
@@ -77,9 +74,8 @@ class TesterTest(unittest.TestCase):
 
     def test_individual_names_are_not_run_twice(self):
         args = [STUBS_CLASS + '.test_empty']
-        parallel_tests, serial_tests = self._find_test_names(args)
-        self.assertEqual(parallel_tests, args)
-        self.assertEqual(serial_tests, [])
+        tests = self._find_test_names(args)
+        self.assertEqual(tests, args)
 
     def test_coverage_works(self):
         # This is awkward; by design, running test-webkitpy -c will