FS-4917 - Remove unused self-serve functionality

This self-serve system was a prototype for constructing forms from lower-level components, built on top of an in-memory "database". Such low-level form consrtuction is not currently within the scope of FAB as a production asset.

We also tidy up usage of the helper functions human_to_kebab_case and human_to_snake_case, which were previously duplicated and imported from the routes file in the self-serve directory.

app/blueprints/fund_builder/templates/index.html

@@ -33,28 +33,6 @@ <h2 class="govuk-heading-s">Fund Configuration (PoC)</h2>
                         <a class="govuk-link" href="{{ url_for("template_bp.view_templates") }}">Manage Templates</a>
                     </li>
                 </ul>
-                <div class="govuk-!-display-none">
-                    <h2 class="govuk-heading-s">Template Management (post PoC)</h2>
-                    <ul class="govuk-body">
-                        <li class="govuk-body">
-                            <a class="govuk-link" href="/">Edit a template Question (text only)</a>
-                        </li>
-                        <li class="govuk-body">
-                            <a class="govuk-link" href="/">Edit a template Page (text only)</a>
-                        </li>
-                        <li class="govuk-body">
-                            <a class="govuk-link" href="/">Edit a template Form (text only)</a>
-                        </li>
-                        <li class="govuk-body">
-                            <a class="govuk-link" href="{{ url_for("self_serve_bp.section") }}">Create a
-                            template Section (Form group)</a>
-                        </li>
-                        <li class="govuk-body">
-                            <a class="govuk-link" href="/">Edit or Delete a
-                            template Section</a>
-                        </li>
-                    </ul>
-                </div>
             </div>
         </div>
     </div>