Remove unused turbo-frame

This was working before because we hadn't been requiring `turbo-rails`
in the engine, but now that we require it, it results in a "Content
missing" error as the response from Sessions#show doesn't include a
matching turbo-frame ID.

app/views/audits1984/sessions/index.html.erb

@@ -1,8 +1,6 @@
 <%= render "audits1984/sessions/filter", filtered_sessions: @filtered_sessions %>
 <%= render "audits1984/sessions/summary", sessions: @sessions %>
 
-<turbo-frame id="sessions">
-  <div class="sessions">
-    <%= render partial: "audits1984/sessions/session", collection: @sessions, cached: true %>
-  </div>
-</turbo-frame>
+<div class="sessions">
+  <%= render partial: "audits1984/sessions/session", collection: @sessions, cached: true %>
+</div>