Reduce the depth of the DOM and simplify the CSS a bit

Remove the main intermediate container. It wasn't acutally serving a purpose.
Remove some of the BEM-style classes that also weren't really doing anything.

layouts/_default/list.html

@@ -4,14 +4,10 @@
       {{ partial "page_header.html" (dict "page" .) }}
     </header>
 
-    {{ with .Content -}}
-      <div class="main--list__content  content">{{ . }}</div>
-    {{- end }}
+    {{- .Content -}}
 
-    <div class="main--list__page-list">
-      {{ range .Pages.ByTitle }}
-        {{ .Render "page_summary" }}
-      {{ end }}
-    </div>
+    {{- range .Pages.ByTitle -}}
+      {{ .Render "page_summary" }}
+    {{- end -}}
   </main>
 {{ end }}