PureLink component needs to be revised

Let's revise the logic of the whole component.
It looks that it's referring some not used siteMetadata like [here](https://github.com/commercetools/commercetools-docs-kit/blob/7c8ee9e97be409f3c395c503531a0d627b12022b/packages/gatsby-theme-docs/src/components/link.js#L200):