Drop ‘preview service name’ page

This page:
- confused users in research
- didn’t communicate what it was intended to (eg the generated email address,
  how your service name would appear in messages)

This commit removes the page so that after typing in the service name the user
is sent straight to the dashboard for their new service.

app/templates/views/add-from-address.html

@@ -1,42 +0,0 @@
-{% extends "withoutnav_template.html" %}
-{% from "components/textbox.html" import textbox %}
-{% from "components/page-footer.html" import page_footer %}
-{% from "components/sms-message.html" import sms_message %}
-{% from "components/email-message.html" import email_message %}
-
-{% block page_title %}
-  Preview your service name – GOV.UK Notify
-{% endblock %}
-
-{% block maincolumn_content %}
-
-  <h1 class="heading-large">
-    Preview your service name
-  </h1>
-
-  <div class="grid-row">
-    <div class="column-two-thirds">
-        {{ sms_message(
-          "{}: we received your payment, thank you".format(service_name),
-          name="Text message",
-          recipient='Sent from 40604'
-        ) }}
-    </div>
-  </div>
-  <div class="grid-row">
-    <div class='column-two-thirds'>
-      {{ email_message(
-        subject="We received your payment, thank you",
-        body="Dear Alice Smith,\n\nThank you for…",
-        from_name=service_name,
-        from_address=from_address,
-        name="Email",
-      ) }}
-    </div>
-  </div>
-
-  <form method="post">
-    {{page_footer('Looks good', back_link=url_for(".add_service"))}}
-  </form>
-
-{% endblock %}