[infra] Fix test runner error when force closing subprocess stdio

The code tried to create the command output object twice in this case.

Change-Id: Icfb413ba329738cb732330d22885f62ccb7a99e2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/150102
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: William Hesse <whesse@google.com>
diff --git a/pkg/test_runner/lib/src/test_case.dart b/pkg/test_runner/lib/src/test_case.dart
index 264d73d..fb4a908 100644
--- a/pkg/test_runner/lib/src/test_case.dart
+++ b/pkg/test_runner/lib/src/test_case.dart
@@ -331,7 +331,6 @@
                 "$maxStdioDelayPassedMessage (command: $command)");
             await stdout.cancel();
             await stderr.cancel();
-            _commandComplete(exitCode);
             return null;
           }).then((_) {
             if (stdout is FileOutputLog) {