pw_presubmit: Use PW_PACKAGE_ROOT

Bug: b/240707084
Change-Id: I367124b9cf35d081249eebd5ee4c25b8d459d16e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/103887
Commit-Queue: Rob Mohr <mohrr@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
diff --git a/pw_presubmit/py/pw_presubmit/cli.py b/pw_presubmit/py/pw_presubmit/cli.py
index 28f751d..08987e9 100644
--- a/pw_presubmit/py/pw_presubmit/cli.py
+++ b/pw_presubmit/py/pw_presubmit/cli.py
@@ -197,8 +197,7 @@
         _OUTPUT_PATH_README.format(repo=root))
 
     if not package_root:
-        package_root = Path(
-            os.environ['_PW_ACTUAL_ENVIRONMENT_ROOT']) / 'packages'
+        package_root = Path(os.environ['PW_PACKAGE_ROOT'])
 
     _LOG.debug('Using environment at %s', output_directory)