Clean up old text message price

Now that the new price is in effect, we don’t need to check the date to
see which price should be displayed to the user.

tests/app/main/views/test_index.py

@@ -359,7 +359,6 @@ def test_font_preload(
 
 
 @pytest.mark.parametrize('current_date, expected_rate', (
-    ('2022-04-30', '1.61'),
     ('2022-05-01', '1.72'),
 ))
 def test_sms_price(