[Mac/GN] Unconditionally write the stamp file in clean_up_old_versions.py.

chrome/tools/build/mac/clean_up_old_versions.py

Index: chrome/tools/build/mac/clean_up_old_versions.py
diff --git a/chrome/tools/build/mac/clean_up_old_versions.py b/chrome/tools/build/mac/clean_up_old_versions.py
index 3849112742a13cad7ec1567ff1ce1c8d089ed496..21d462c670a6e307a82ee65e115432f165628f91 100644
--- a/chrome/tools/build/mac/clean_up_old_versions.py
+++ b/chrome/tools/build/mac/clean_up_old_versions.py
@@ -10,12 +10,10 @@ import sys
 
 def CleanUpOldVersions(path_to_app, keep_version, stamp_path):
   versions_dir = os.path.join(path_to_app, 'Contents', 'Versions')
-  if not os.path.exists(versions_dir):
-    return
-
-  for version in os.listdir(versions_dir):
-    if version != keep_version:
-      shutil.rmtree(os.path.join(versions_dir, version))
+  if os.path.exists(versions_dir):
+    for version in os.listdir(versions_dir):
+      if version != keep_version:
+        shutil.rmtree(os.path.join(versions_dir, version))
 
   open(stamp_path, 'w').close()
   os.utime(stamp_path, None)