Revert "Update gsutil to use gsutil version 4.68"

This reverts commit 8edc960e9a.

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>

gsutil.py.vpython3

@@ -1,19 +0,0 @@
-# vpython VirtualEnv protobuf for "gsutil".
-#
-# See:
-# https://chromium.googlesource.com/infra/luci/luci-go/+/HEAD/vpython/api/vpython/spec.proto
-#
-# This is a "vpython" VirtualEnv specification applied to invocations of "gsutil"
-# by the bootstrap wrapper, "gsutil.py". It ensures that any Python distribution
-# has the expected Python packages installed.
-#
-# This is specifically relevant on Google Compute Engine invocations of
-# "gsutil", where a stock system-deployed file in "/etc/" explicitly specifies
-# that the "google_compute_engine" and "boto" Python packages are available.
-
-python_version: "3.8"
-
-wheel: <
-  name: "infra/python/wheels/crcmod/${vpython_platform}"
-  version: "version:1.7.chromium.3"
->