Don’t fill out address line 3 in the example

Address line 3 is optional. Currently the only way we have of indicating
to users what is/isn’t optional is by using the example. Which probably
isn’t ideal, but should at least be correct.

app/main/views/send.py

@@ -77,7 +77,6 @@ def get_example_letter_address(key):
     return {
         'address line 1': 'A. Name',
         'address line 2': '123 Example Street',
-        'address line 3': 'Example town',
         'postcode': 'XM4 5HQ'
     }.get(key, '')