Cleanup dual target and mono code

Fixes #1893
Fixes #1808

src/NzbDrone.Core/Update/UpdatePackage.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using NzbDrone.Common.EnvironmentInfo;
 
 namespace NzbDrone.Core.Update
@@ -12,6 +12,5 @@ namespace NzbDrone.Core.Update
         public UpdateChanges Changes { get; set; }
         public string Hash { get; set; }
         public string Branch { get; set; }
-        public PlatformType Runtime { get; set; }
     }
 }