Remove /admin/dashboard page.

This page was just a combination of the forum listing and the bulk
update requests listing. It got zero hits in the last week.

test/functional/admin/dashboards_controller_test.rb

@@ -1,16 +0,0 @@
-require 'test_helper'
-
-class Admin::DashboardsControllerTest < ActionDispatch::IntegrationTest
-  context "The admin dashboard controller" do
-    setup do
-      @admin = create(:admin_user)
-    end
-
-    context "show action" do
-      should "render" do
-        get_auth admin_dashboard_path, @admin
-        assert_response :success
-      end
-    end
-  end
-end