Fix the downloader for using Realm native

ios/App/Shared/models/DownloadItem.swift

@@ -73,7 +73,6 @@ class DownloadItemPart: Object, Codable {
     @Persisted var uri: String?
     @Persisted var destinationUri: String?
     @Persisted var progress: Double = 0
-    var task: URLSessionDownloadTask?
     
     private enum CodingKeys : String, CodingKey {
         case id, filename, itemTitle, completed, moved, failed, progress

ios/App/Shared/util/Database.swift

@@ -164,11 +164,6 @@ class Database {
         return try! realm.write { realm.add(downloadItem, update: .modified) }
     }
     
-    public func updateDownloadItemPart(_ part: DownloadItemPart) {
-        let realm = try! Realm()
-        return try! realm.write { realm.add(part, update: .modified) }
-    }
-    
     public func removeDownloadItem(_ downloadItem: DownloadItem) {
         let realm = try! Realm()
         return try! realm.write { realm.delete(downloadItem) }