Adding a rule that turns off assembly info generation for attributes already defined when migrating.

TestAssets/TestProjects/AppWithAssemblyInfo/Program.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace ConsoleApp1
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+        }
+    }
+}

TestAssets/TestProjects/AppWithAssemblyInfo/Properties/AssemblyInfo.cs

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+using System.Reflection;
+using System.Resources;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("ConsoleApp1")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCopyright("")]
+[assembly: AssemblyDescription("")]
+[assembly: AssemblyFileVersion("")]
+[assembly: AssemblyInformationalVersion("")]
+[assembly: AssemblyTitle("")]
+[assembly: AssemblyVersion("1.0.0")]
+[assembly: NeutralResourcesLanguage("")]
+
+// Setting ComVisible to false makes the types in this assembly not visible
+// to COM components.  If you need to access a type in this assembly from
+// COM, set the ComVisible attribute to true on that type.
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("ab699746-eb43-467d-ab46-6095b4de9722")]

TestAssets/TestProjects/AppWithAssemblyInfo/project.json

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+{
+  "version": "1.0.0-*",
+  "buildOptions": {
+    "emitEntryPoint": true
+  },
+
+  "dependencies": {
+    "Microsoft.NETCore.App": {
+      "type": "platform",
+      "version": "1.0.1"
+    }
+  },
+
+  "frameworks": {
+    "netcoreapp1.0": {
+      "imports": "dnxcore50"
+    }
+  }
+}