Prevent loading wiki content for destroy and diff actions

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/81513 we
add a param to avoid loading the wiki page content. In
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71753 we
avoid loading the content for the show and history actions.

But there are other actions where we don't need the wiki page
content and we still load it. These actions are `diff`
and `destroy`.

Changelog: performance

app/controllers/concerns/wiki_actions.rb

@@ -312,7 +312,7 @@ module WikiActions
   end
 
   def load_content?
-    return false if params[:action] == 'history'
+    return false if %w[history destroy diff].include?(params[:action])
     return false if params[:action] == 'show' && Feature.enabled?(:wiki_async_load, container, default_enabled: :yaml)
 
     true

spec/support/shared_examples/controllers/wiki_actions_shared_examples.rb

@@ -150,6 +150,7 @@ RSpec.shared_examples 'wiki controller actions' do
         expect(response).to render_template('shared/wikis/diff')
         expect(assigns(:diffs)).to be_a(Gitlab::Diff::FileCollection::Base)
         expect(assigns(:diff_notes_disabled)).to be(true)
+        expect(assigns(:page).content).to be_empty
       end
     end
 
@@ -475,9 +476,13 @@ RSpec.shared_examples 'wiki controller actions' do
     context 'when page exists' do
       shared_examples 'deletes the page' do
         specify do
-          expect do
-            request
-          end.to change { wiki.list_pages.size }.by(-1)
+          aggregate_failures do
+            expect do
+              request
+            end.to change { wiki.list_pages.size }.by(-1)
+
+            expect(assigns(:page).content).to be_empty
+          end
         end
       end