Made the LocalDatabase constructor protected to ensure that derived classes won't call the obsolete warning throwing constructor.

Duplicati/Library/Main/Database/LocalDatabase.cs

@@ -90,7 +90,7 @@ namespace Duplicati.Library.Main.Database
         public bool ShouldCloseConnection { get; set; }
 
         // Constructor is private to force use of CreateLocalDatabaseAsync
-        private LocalDatabase() { }
+        protected LocalDatabase() { }
 
         // Arguments are not used, but are required to match the constructor signatures
         [Obsolete("Calling the constructor will throw an exception. Use the CreateLocalDatabaseAsync or CreateLocalDatabase functions instead")]

Duplicati/Library/Main/Database/LocalRestoreDatabase.cs

@@ -59,8 +59,6 @@ namespace Duplicati.Library.Main.Database
 
         public DateTime RestoreTime { get { return m_restoreTime; } }
 
-        private LocalRestoreDatabase() { }
-
         public static async Task<LocalRestoreDatabase> CreateAsync(string path, long pagecachesize)
         {
             var db = new LocalRestoreDatabase();