Deleting Event Handlers
When you delete a component from a form using the Form Designer, the Code Editor removes the component from the form's type declaration. It does not, however, delete any associated methods from the unit file, since these methods mighty still be called by other components on the form.
You can manually delete a method—such as an event handler—but if you do so, be sure to delete both the method declaration and implementation. Otherwise you'll get a compiler error when you build your project.