[ package:vm_service ] Fix bad merge resulting in double stream subscriptions

Fixes https://github.com/dart-lang/sdk/issues/48403
Fixes https://github.com/dart-lang/sdk/issues/48340
Fixes https://github.com/dart-lang/sdk/issues/47734

TEST=Existing

Change-Id: Ie844642d5e50cf455c115b6d3af1c1dc30e194a6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/233120
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>
diff --git a/pkg/vm_service/test/common/test_helper.dart b/pkg/vm_service/test/common/test_helper.dart
index 4100c68..8415c74 100644
--- a/pkg/vm_service/test/common/test_helper.dart
+++ b/pkg/vm_service/test/common/test_helper.dart
@@ -349,10 +349,6 @@
     });
     await service.streamListen(EventStreams.kIsolate);
 
-    await service.streamListen(EventStreams.kIsolate);
-
-    await service.streamListen(EventStreams.kIsolate);
-
     // The isolate may have started before we subscribed.
     vm = await service.getVM();
     if (vmIsolates.isNotEmpty) {