Revert "Allow nested sub-menus in the ActionMenu component" (#3638)

Co-authored-by: jonrohan <54012+jonrohan@users.noreply.github.com>

Author: jonrohan

.changeset/forty-ghosts-admire.md

@@ -1,3 +1,28 @@
 <%= render Primer::BaseComponent.new(**@system_arguments) do %>
-  <%= render(@primary_menu) %>
+  <focus-group direction="vertical" mnemonics retain>
+    <%= render(@overlay) do |overlay| %>
+      <% overlay.with_body(padding: :none) do %>
+        <% if @src.present? %>
+          <%= render(Primer::Alpha::IncludeFragment.new(src: @src, loading: preload? ? :eager : :lazy, "data-target": "action-menu.includeFragment")) do %>
+            <%= render(Primer::Alpha::ActionMenu::List.new(id: "#{@menu_id}-list", menu_id: @menu_id)) do |list| %>
+              <% list.with_item(
+                aria: { disabled: true },
+                content_arguments: {
+                  display: :flex,
+                  align_items: :center,
+                  justify_content: :center,
+                  text_align: :center,
+                  autofocus: true
+                }
+              ) do %>
+                <%= render Primer::Beta::Spinner.new(aria: { label: "Loading content..." }) %>
+              <% end %>
+            <% end %>
+          <% end %>
+        <% else %>
+          <%= render(@list) %>
+        <% end %>
+      <% end %>
+    <% end %>
+  </focus-group>
 <% end %>