Do not list removed Markdown files

[gr2m]

When I created https://github.com/octokit/rest.js/pull/1085, mardownify listed lib/endpoint/README.md which was removed compared to master. I since changed the base to next so it no longer is edited in the PR

[owenvoke]

In theory it should be possible to add && file.status !== 'removed' to https://github.com/hiimbex/markdownify/blob/37ff22a9c89747bce8fee11751814aa7238e8343/index.js#L4

However, when trying this, file only contains the filename property, unlike in the API documentation. 🤔

[hiimbex]

That solution sounds perfect to me @pxgamer! Not sure why file.status wouldn't exist though 🤔

PRs welcome!