Revert "Update gsutil to use gsutil version 4.68"

This reverts commit 8edc960e9acbaedbff28e323e77a4129817266b3.

Reason for revert: potentially breaking chromeos builders

Original change's description:
> Update gsutil to use gsutil version 4.68
>
> We can't yet upgrade to version 5.x since it's only py3 compatbile and
> some builders still rely on running gsutil with py2.
>
> R=​gavinmak@google.com
>
> Bug: 1184108
> Change-Id: I002cc3625a2184ab42383b88a014c0631d1a33ee
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3508516
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

Bug: 1184108
Change-Id: I40ce645ebd928c63116012353c632026c787b154
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3514508
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
diff --git a/gsutil.py b/gsutil.py
index 522ddb3..61aaafe 100755
--- a/gsutil.py
+++ b/gsutil.py
@@ -34,7 +34,7 @@
 
 IS_WINDOWS = os.name == 'nt'
 
-VERSION = '4.68'
+VERSION = '4.28'
 
 
 class InvalidGsutilError(Exception):
@@ -166,7 +166,9 @@
   assert sys.platform != 'cygwin'
 
   cmd = [
-      sys.executable,
+      'vpython',
+      '-vpython-spec', os.path.join(THIS_DIR, 'gsutil.vpython'),
+      '--',
       gsutil_bin
   ] + args_opt + args
   return subprocess.call(cmd, shell=IS_WINDOWS)