templates: Remove logout form shared template.

It's sufficiently tiny that the shared code benefits don't justify the
cost, given that we plan to move index.html to a different templating
system soon.

templates/zerver/app/index.html

@@ -177,7 +177,10 @@
         </div>
     </div>
     {% include "zerver/app/invite_user.html" %}
-    {% include "zerver/app/logout.html" %}
+    <div class="hidden">
+        <form id="logout_form" action="/accounts/logout/" method="POST">{{ csrf_input }}
+        </form>
+    </div>
     {% include "zerver/app/deprecation_notice.html" %}
     {% include "zerver/app/about-zulip.html" %}
     <div id="user-profile-modal-holder"></div>

templates/zerver/app/logout.html

@@ -1,4 +0,0 @@
-<div class="hidden">
-    <form id="logout_form" action="/accounts/logout/" method="POST">{{ csrf_input }}
-    </form>
-</div>

templates/zerver/portico-header-dropdown.html

@@ -11,7 +11,10 @@
             </a>
         </li>
         <li class="logout">
-            {% include 'zerver/app/logout.html' %}
+            <div class="hidden">
+                <form id="logout_form" action="/accounts/logout/" method="POST">{{ csrf_input }}
+                </form>
+            </div>
             <a href="#logout">
                 <i class="fa fa-sign-out"></i>
                 Log out

tools/check-templates

@@ -62,6 +62,7 @@ def check_html_templates(templates: Iterable[str], all_dups: bool, fix: bool) ->
             "top_navbar",
             "id_email",
             "id_terms",
+            "logout_form",
             "send_confirm",
             "register",
             "footer",