Make the ‘no recipient column’ error more concise

Word salad.

app/templates/views/check.html

@@ -57,7 +57,7 @@
     <div class="bottom-gutter">
       {% call banner_wrapper(type='dangerous') %}
         <h1 class='banner-title'>
-          Your file needs to have {{ recipients.recipient_column_headers | formatted_list(
+          Your file needs {{ recipients.recipient_column_headers | formatted_list(
             prefix='a column called',
             prefix_plural='columns called'
           ) }}

tests/app/main/views/test_send.py

@@ -130,7 +130,7 @@ def test_upload_csvfile_with_errors_shows_check_page_with_errors(
             +447700900986
         """,
         (
-            'Your file needs to have a column called ‘phone number’ '
+            'Your file needs a column called ‘phone number’ '
             'Your file has columns called ‘telephone’ and ‘name’. '
             'Skip to file contents'
         )