Remove test.test_support.guard_warnings_filter.
test.test_support.catch_warning is more full-featured and provides the same
functionality.

Since guard_warnings_filter was added in 2.6 there is no
backwards-compatibility issues.
diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index 283806f..cca6329 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -61,7 +61,7 @@
     def test_options(self):
         # Uses the private _setoption() function to test the parsing
         # of command-line warning arguments
-        with test_support.guard_warnings_filter():
+        with test_support.catch_warning():
             self.assertRaises(warnings._OptionError,
                               warnings._setoption, '1:2:3:4:5:6')
             self.assertRaises(warnings._OptionError,