removed sentence since functions can have state (reactjs#1878)

With introduction of hooks, that statement is not valid anymore

Author: saranshkataria

content/docs/state-and-lifecycle.md

@@ -72,8 +72,6 @@ To implement this, we need to add "state" to the `Clock` component.
 
 State is similar to props, but it is private and fully controlled by the component.
 
-We [mentioned before](/docs/components-and-props.html#functional-and-class-components) that components defined as classes have some additional features. Local state is exactly that: a feature available only to classes.
-
 ## Converting a Function to a Class {#converting-a-function-to-a-class}
 
 You can convert a function component like `Clock` to a class in five steps: