Revert "CHROMIUM: Update .vpython3 spec"

This reverts commit 212452c.

Reason for revert: unidiff is needed by zephyr_check_compliance_unittest

Original change's description:
> CHROMIUM: Update .vpython3 spec
>
> Add unidiff package required by Zephyr since this CL:5779571.
>
> You have to run python scripts as `vpython script.py` instead to get
> this environment.
>
> BUG=b:320527549
> TEST=zmake build -a
>
> Change-Id: I57e6b9fd8cb0756baaa0bdf1fd11aaab2af801e4
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5785813
> Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>
> Tested-by: Dawid Niedźwiecki <dawidn@google.com>
> Commit-Queue: Dawid Niedźwiecki <dawidn@google.com>

BUG=b:320527549

Change-Id: Iebfa3bf229f6ac54f1d24edbeace21f043e1f4a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5790976
Commit-Queue: Dawid Niedźwiecki <dawidn@google.com>
Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>
Tested-by: Dawid Niedźwiecki <dawidn@google.com>

.vpython3

@@ -67,7 +67,3 @@ wheel: <
   name: "infra/python/wheels/pyelftools-py2_py3"
   version: "version:0.29"
 >
-wheel: <
-  name: "infra/python/wheels/unidiff-py2_py3"
-  version: "version:0.7.5"
->