Remove unnecessary render calls

Rails will render the appropriate view by default, so there's no need to
 call render from within the controller action method to render the
 default view.

In `confirm_destroy`, the return is unnecessary now that there is no
 more code after the potential redirect.

app/controllers/admin/document_collection_groups_controller.rb

@@ -11,15 +11,12 @@ def index
         :non_whitehall_link,
       ],
     )
-
-    render :index
   end
 
   def show; end
 
   def new
     @group = @collection.groups.build
-    render :new
   end
 
   def create
@@ -33,9 +30,7 @@ def create
     end
   end
 
-  def edit
-    render :edit
-  end
+  def edit; end
 
   def update
     @group.update!(document_collection_group_params)
@@ -65,9 +60,7 @@ def destroy
   end
 
   def confirm_destroy
-    redirect_to admin_document_collection_groups_path(@collection) and return unless @collection.groups.many?
-
-    render :confirm_destroy
+    redirect_to admin_document_collection_groups_path(@collection) unless @collection.groups.many?
   end
 
 private