You can't disable the new tab page suggestions in Chrome 58 Dev on Android as it seems that one of the flags that was needed to turn this feature for recommended articles off has disappeared in this particular version of Chrome on the dev channel. One of the flags that users could disable which would lead to disabling the recommended articles that pop up when you open a new tab inside of Chrome is the #enable-ntp-snippets flag, and this no longer looks to be a part of the list of Chrome flags in this version. Without it, disabling the recommended articles isn't possible.
It's unclear if Google is working towards making it impossible to disable the recommended articles from the new tab page or if this particular flag has just been removed from the dev channel for the time being, and unfortunately this is something that won't have more detail right now. If the same flag is absent from Chrome 58 beta at some point though, once Chrome 58 moves out of the dev channel, then it will likely be more clear on what Google's plans are for recommended articles on the new tab page going forward and whether or not they want to make it a mandatory part of Chrome.
If you aren't too familiar with the recommended articles on the new tab page, they're articles and web page suggestions that Google is recommending in Chrome the moment you open up a new tab on your mobile device. These aren't immediately noticeable if the first thing you do is type in the Google Search bar or move to open a bookmark, but if you scroll up on the screen you'll see all the recommended articles that Google thinks you might enjoy. This feature likely doesn't bother many users, but there are likely many users who also don't care for it, and were happy to have some way to disable these even if it meant rooting around in the Chrome flags list to get it done. The recommended articles aren't so bad if you want multiple ways to get access to the content you might enjoy reading on the web, especially since the suggestions that are there are based on your interests. Google already offers a similar experience to getting at this content in Google Now though, which may be why some people don't want it in Chrome as well.