StyleGuide: Update frontend style guide (#52471)

We should not explicitly type the return type for React functional components.

contribute/style-guides/frontend.md

@@ -351,7 +351,7 @@ static defaultProps: Partial<Props> = { ... }
 We recommend using named regular functions when creating a new react functional component.
 
 ```typescript
-export function Component(props: Props): ReactElement { ... }
+export function Component(props: Props) { ... }
 ```
 
 ## State management