Remove deprecated package-root flag.

Change-Id: I519d4751b596751f930884d0320c60dbdbcbce48
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/106202
Commit-Queue: Bob Nystrom <rnystrom@google.com>
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Reviewed-by: William Hesse <whesse@google.com>
diff --git a/pkg/test_runner/test/test_runner_test.dart b/pkg/test_runner/test/test_runner_test.dart
index e4cdc46..79305bc 100644
--- a/pkg/test_runner/test/test_runner_test.dart
+++ b/pkg/test_runner/test/test_runner_test.dart
@@ -24,9 +24,7 @@
 final LONG_TIMEOUT = 30;
 
 List<String> packageOptions() {
-  if (Platform.packageRoot != null) {
-    return <String>['--package-root=${Platform.packageRoot}'];
-  } else if (Platform.packageConfig != null) {
+  if (Platform.packageConfig != null) {
     return <String>['--packages=${Platform.packageConfig}'];
   } else {
     return <String>[];