Fix the test count in the WPT grouping_formatter

The internal WPT API seems to have changed again, so we must revert the
previous change here to get the correct test count.

tests/wpt/grouping_formatter.py

@@ -105,7 +105,7 @@ def build_status_line(self):
             return new_display + "No tests running.\n"
 
     def suite_start(self, data):
-        self.number_of_tests = sum(len(tests) for tests in data["tests"].itervalues())
+        self.number_of_tests = len(data["tests"])
         self.start_time = data["time"]
 
         if self.number_of_tests == 0: