Remove old #import, #source, and #library syntax from tests/standalone.

tests/standalone/io/process_stderr_test.dart

Index: tests/standalone/io/process_stderr_test.dart
diff --git a/tests/standalone/io/process_stderr_test.dart b/tests/standalone/io/process_stderr_test.dart
index 34cc67249f5309a793fa4d440bfafde8b3059c30..ebb97d49ede40126aaa3ef77b549bbbe275f6972 100644
--- a/tests/standalone/io/process_stderr_test.dart
+++ b/tests/standalone/io/process_stderr_test.dart
@@ -9,10 +9,10 @@
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
-#import('dart:io');
-#import('dart:math');
+import "dart:io";
+import "dart:math";
 
-#source('process_test_util.dart');
+part "process_test_util.dart";
 
 void test(Future<Process> future, int expectedExitCode) {
   future.then((process) {