refactor: remove unused handleAddCheckbox function in FormsSection

- Deleted the `handleAddCheckbox` function from `FormsSection` as it was not being utilized, streamlining the component's code.

src/components/ui-showcase/sections/FormsSection.tsx

@@ -19,15 +19,6 @@ export function FormsSection() {
     { id: '3', text: 'Tâche en cours', isChecked: false, type: 'task' }
   ]);
 
-  const handleAddCheckbox = (text: string) => {
-    const newItem: CheckboxItemData = {
-      id: Date.now().toString(),
-      text,
-      isChecked: false,
-      type: 'task'
-    };
-    setCheckboxItems(prev => [...prev, newItem]);
-  };
 
   const handleToggleCheckbox = (id: string) => {
     setCheckboxItems(prev =>