Remove Storybook's demo stories

[MAILPOET-2770]

assets/js/src/storybook_demo/_stories/button.tsx

@@ -1,23 +0,0 @@
-import React from 'react';
-import { action } from '@storybook/addon-actions';
-import { Button } from '@storybook/react/demo';
-
-export default {
-  title: 'Button',
-  component: Button,
-};
-
-export const Text = () => (
-  <Button onClick={action('clicked')}>
-    Hello Button
-    <img src="/assets/img/handle.png" alt="" />
-  </Button>
-);
-
-export const Emoji = () => (
-  <Button onClick={action('clicked')}>
-    <span role="img" aria-label="so cool">
-      😀 😎 👍 💯
-    </span>
-  </Button>
-);

assets/js/src/storybook_demo/_stories/welcome.tsx

@@ -1,14 +0,0 @@
-import React from 'react';
-import { linkTo } from '@storybook/addon-links';
-import { Welcome } from '@storybook/react/demo';
-
-export default {
-  title: 'Welcome',
-  component: Welcome,
-};
-
-export const ToStorybook = () => <Welcome showApp={linkTo('Button')} />;
-
-ToStorybook.story = {
-  name: 'to Storybook',
-};