Eliminate old style import from language tests

tests/language/source_self_negative_test.dart

Index: tests/language/source_self_negative_test.dart
===================================================================
--- tests/language/source_self_negative_test.dart	(revision 15598)
+++ tests/language/source_self_negative_test.dart	(working copy)
@@ -4,9 +4,9 @@
 
 // Dart test program importing the core library explicitly.
 
-#library("SourceSelfNegativeTest");
-#source("source_self_negative_test.dart");
+library SourceSelfNegativeTest;
+part "source_self_negative_test.dart";  // recursive reference to self.
 
 main() {
-  print('should not be able to #source a file with directives');
+  print('should not be able to recursively include self as library part');
 }