Unfortunately, there is no way to remove them other than to drop the project's target SDK to 23.3 and reinstall all the Xamarin Android Support packages using v23.3.
Rest assured that it doesn't have any impact on the result of the compilation or the run time application because
I can confirm UI for Xamarin works with newer version of Xamarin.Android.
Microsoft or Xamarin doesn't offer a way to ignore those warnings from your project, there are suggestions on using PRAGMA definitions and adding warning codes to the "Ignore" box in the project's Build settings, but I've found this doesn't remove all of them either.
The reason you're seeing them is because we compile Telerik UI for Xamarin to support a minimum Android SDK level of 23.3. This happens with any 3rd party package that is compiled with an older version of the Xamarin Android Support Libraries.
We do plan on updating the minimum version, but not to the latest version (because this would break every project that isn't targeting the latest version of Android). Even if we did update to the latest, it would be a temporary solution because the next time Xamarin releases an update to the support libraries, you'll see the warnings again. Ultimately, there needs a be a solution from Microsoft on a way to disable these warnings.
Lance | Tech Support Engineer, Sr.
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