Remove attr from Usage with CSS Modules docs (#206)

docs/css-modules.md

@@ -8,39 +8,3 @@ emotion works well with CSS Modules but it requires a bit of configuration.
 
 - [Example webpack config](../example/webpack.config.js)
 - [Example usage of CSS Modules with emotion](../example/src/markdown/index.js)
-
-### attr
-
-The [attr](https://developer.mozilla.org/en-US/docs/Web/CSS/attr) CSS function is supported in
-a basic capacity.
-
-```css
-/* get value from `width` prop */
-width: attr(width vw);
-
-/* specify type or unit to apply to value */
-width: attr(width vw);
-
-/* fallback value if props.width is falsey */
-width: attr(width vw, 50);
-```
-
-```jsx
-const H1 = styled.h1`
-  font-size: attr(fontSize px);
-  margin: attr(margin rem, 4);
-  font-family: sans-serif;
-  color: attr(color, ${colors.pink[5]});
-  @media (min-width: 680px) {
-    color: attr(desktopColor);
-  }
-`
-
-const Title = ({ title, scale }) => {
-  return (
-    <H1 fontSize={16 * scale} desktopColor={colors.gray[5]}>
-      {title}
-    </H1>
-  )
-}
-```