Cleanup todos-flow container (#3365)

Remove unused `input` property.

Author: kootoopas

examples/todos-flow/src/containers/AddTodo.js

@@ -16,7 +16,6 @@ export type State = {
 };
 
 class AddTodo extends Component<Props, State> {
-  input: HTMLInputElement;
   state = {
     value: ''
   };