Test: Removed date-sensitive test

- Removed test that assumes 'due:yesterday' matches '+MONTH', which of course
  is not true for the 1st of the month.

test/tag.t

@@ -281,19 +281,17 @@ class TestVirtualTags(TestCase):
         self.assertNotIn("completed", out)
         self.assertNotIn("deleted", out)
         self.assertNotIn("minimal", out)
-        self.assertIn("maximal", out)
         self.assertNotIn("blocked", out)
         self.assertIn("due_eom", out)
-        # Ignore due_eow, which may be a different month.
+        # Ignore maximal, due_eow, which may be a different month.
 
         code, out, err = self.t("-MONTH all")
         self.assertIn("completed", out)
         self.assertIn("deleted", out)
         self.assertIn("minimal", out)
-        self.assertNotIn("maximal", out)
         self.assertIn("blocked", out)
         self.assertNotIn("due_eom", out)
-        # Ignore due_eow, which may be a different month.
+        # Ignore maximal, due_eow, which may be a different month.
 
     def test_virtual_tag_WEEK(self):
         """Verify 'WEEK' appears when expected"""