C#: Base the asp/basic tests on stubs only.

Author: michaelnebel

csharp/ql/test/library-tests/asp/basic/CodeBehind.expected

@@ -1,2 +1,2 @@
-| script.aspx:1:1:1:75 | <%@Page ...%> | Test.cs:11:11:11:24 | CodeBehindPage |
-| test.aspx:1:1:1:56 | <%@Page ...%> | Test.cs:11:11:11:24 | CodeBehindPage |
+| script.aspx:1:1:1:75 | <%@Page ...%> | Test.cs:13:11:13:24 | CodeBehindPage |
+| test.aspx:1:1:1:56 | <%@Page ...%> | Test.cs:13:11:13:24 | CodeBehindPage |

csharp/ql/test/library-tests/asp/basic/Test.cs

@@ -1,4 +1,6 @@
-// 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
 
 using System;
 using System.Web;