Let users on email auth delete their mobile numbers

Sometimes users ask us to delete their mobile numbers for them.

If those users are on email auth, they should be able to
delete their number themselves.

This will save them writing a support ticket and save us
going into the database.

app/templates/views/user-profile/change.html

@@ -20,9 +20,20 @@
     <div class="govuk-grid-column-three-quarters">
       {% call form_wrapper() %}
         {{ form_field(error_message_with_html=True) }}
-        {{ page_footer('Save') }}
+        {% if current_user.auth_type == 'email_auth' %}
+          {{ page_footer(
+            'Save',
+            delete_link=url_for(
+              'main.user_profile_mobile_number_delete',
+              user_id=current_user.id
+            ),
+            delete_link_text='Delete your number'
+            )
+          }}
+        {% else %}
+          {{ page_footer('Save')}}
+        {% endif %}
       {% endcall %}
     </div>
   </div>
-
 {% endblock %}