C#: Only include source code (and not stubs) in the remote flow source test.

Author: michaelnebel

csharp/ql/test/library-tests/dataflow/flowsources/remote/remoteFlowSource.ql

@@ -1,4 +1,5 @@
 import semmle.code.csharp.security.dataflow.flowsources.Remote
 
 from RemoteFlowSource source
+where source.getLocation().getFile().fromSource()
 select source, source.getSourceType()