As far as I know, you cannot remove YouTube's user interface when you embed it in your app.
As you can surely understand, there are monetary reasons behind it such as ads, statistics and so forth. Also the content-creators i.e. the good people who are making and distributing the videos using the eco-system of YouTube rely on the number of views, subscriptions and affiliate links so they can get feedback and perhaps earn some money. Other reasons can be Intellectual Property issues such as distribution rights etc. This is why YouTube won't permit bypassing the YouTube interface.
But as I already wrote, you should not use the YouTube-DL wrapper in an app published on Google Play Store as the app would probably be removed and you might even be banned. It is probably OK for an app which you distribute elsewhere.