Remove the get_phrase_cfws_only_raises test

This test's name does not start with test_, which prevents it from
running. Apparently it was accidentally added this way.

None of the callers of get_phrase() assume it can raise exceptions, so
simply dropping the test seems best. The fact that the phrase is invalid
still gets recorded in defects.

Author: elenril

Lib/test/test_email/test__header_value_parser.py

@@ -1031,10 +1031,6 @@ def test_get_phrase_ending_with_obsolete(self):
         self.assertEqual(len(phrase), 4)
         self.assertEqual(phrase[3].comments, ['with trailing comment'])
 
-    def get_phrase_cfws_only_raises(self):
-        with self.assertRaises(errors.HeaderParseError):
-            parser.get_phrase(' (foo) ')
-
     # get_local_part
 
     def test_get_local_part_simple(self):