C#: Use stubs for the CWE-601 testcase.

Author: michaelnebel

csharp/ql/test/query-tests/Security Features/CWE-601/UrlRedirect/options

@@ -1,2 +1,3 @@
-semmle-extractor-options: /r:System.Private.Uri.dll
-semmle-extractor-options: ${testdir}/../../../../resources/stubs/System.Web.cs /r:System.Collections.Specialized.dll
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj
+semmle-extractor-options: ${testdir}/../../../../resources/stubs/System.Web.cs

csharp/ql/test/query-tests/Security Features/CWE-601/UrlRedirect/stubs.cs

@@ -167,16 +167,3 @@ public struct StringValues : System.IEquatable<string[]>, System.IEquatable<stri
 }
 }
 }
-namespace System
-{
-// Generated from `System.Uri` in `System.Private.Uri, Version=4.0.4.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a`
-public class Uri : System.Runtime.Serialization.ISerializable
-{
-    public Uri(string uriString) => throw null;
-    public override bool Equals(object comparand) => throw null;
-    public override int GetHashCode() => throw null;
-    public override string ToString() => throw null;
-    void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo serializationInfo, System.Runtime.Serialization.StreamingContext streamingContext) => throw null;
-}
-
-}