Revert "Add protobuf-py2_py3 3.13.0 to .vpython."

This reverts commit 9b53c2983260a210ba4f04510759bc56d5a2285e.

Reason for revert: It hasn't fixed the issue.

Original change's description:
> Add protobuf-py2_py3 3.13.0 to .vpython.
>
> Starting from https://webrtc-review.googlesource.com/c/src/+/194081,
> WebRTC's protobuf are using version 3.13.0.1+ but when running on
> bots, we see errors that are probably caused by a version mismatch, see
> https://ci.chromium.org/p/webrtc/builders/perf/Perf%20Linux%20Trusty/4597.
>
> This CL updates WebRTC's .vpython to use protobuf 3.13.0.
>
> TBR=kwiberg@webrtc.org
>
> No-Try: True
> Bug: None
> Change-Id: I6bc5e71bacc67dbd9299a9588ddf826778451949
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/194143
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Reviewed-by: Andrey Logvin <landrey@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#32642}

TBR=mbonadei@webrtc.org,kwiberg@webrtc.org,landrey@webrtc.org

Change-Id: I8d16d30bbe922b826f4839af941168a4d9b26318
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: None
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/194260
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32648}

.vpython

@@ -66,10 +66,6 @@ wheel: <
   name: "infra/python/wheels/mock-py2_py3"
   version: "version:2.0.0"
 >
-wheel: <
-  name: "infra/python/wheels/protobuf-py2_py3"
-  version: "version:3.13.0"
->
 wheel: <
   name: "infra/python/wheels/requests-py2_py3"
   version: "version:2.13.0"