SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.3 - https://docs.sitefinity.com/for-developers-delete-video-libraries

DeleteVideoLibraries_DeleteAllVideoLibrariesNativeAPI.cs

using System.Linq;
using Telerik.Sitefinity.Libraries.Model;
using Telerik.Sitefinity.Modules.Libraries;

namespace SitefinityWebApp
{
    public class DeleteVideoLibraries_DeleteAllVideoLibrariesNativeAPI
    {
        private void DeleteAllVideoLibrariesNativeAPI()
        {
            LibrariesManager manager = LibrariesManager.GetManager();

            var videoLibraries = manager.GetVideoLibraries().ToList();

            foreach (VideoLibrary library in videoLibraries)
            {
                manager.DeleteVideoLibrary(library);
            }

            manager.SaveChanges();
        }
    }
}