Fix community list template title

The community list template was expecting a context variable called
page_title to be used for rendering the page title even though the view
using the template doesn't populate such a variable.

Replace the variable usage with a constant value in the template
directly.

django/thunderstore/community/templates/community/community_list.html

@@ -8,7 +8,7 @@
 {% cache 300 templates.community.list %}
 
 <div class="row">
-    <h3 class="col-12 mt-4">{{ page_title }}</h3>
+    <h3 class="col-12 mt-4">All communities</h3>
 </div>
 
 {% if object_list %}