Remove blue from column headings on send page

While the blue should help reinforce the relationship between the placeholders
and the column headings, it makes the column headings very busy visually, and
less like column headings. Which make the relationship harder to see. I think.

app/templates/views/send-test.html

@@ -40,9 +40,7 @@
     {% call(item, row_number) list_table(
       example,
       caption="Fill in the {}".format('field' if template.placeholders|length == 1 else 'fields'),
-      field_headings=[
-        '<span class="placeholder">{}</span>'.format(recipient_column)|safe
-      ] + template.placeholders_as_markup|list
+      field_headings=[recipient_column] + template.placeholders|list
     ) %}
       {% for column in item %}
         {% call field() %}