Revert "[exec2] Fix Windows test on go1.16."
Revert "[exec2] Fix Windows test on go1.16."

This reverts commit ac503fe8c6bd5055091a7f5aecd832f22ce5425f.

Reason for revert: reverting because we are back to go.15 :(

Original change's description:
> [exec2] Fix Windows test on go1.16.
>
> Looks like CTRL_BREAK_EVENT event is now reported as exit
> code 0xC000013A aka 3221225786 aka "The application terminated
> as a result of a CTRL+C."
>
> R=​iannucci@chromium.org, 71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org
>
> Change-Id: I5ebe241f4d17b12b237943fa5754a4a72ffed88c
> Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2698658
> Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
> Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
> Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>

Change-Id: Ic58dc4d0ef12608c75d9fba9fb4d849c61e525b0
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2703411
Bot-Commit: Rubber Stamper <d516c4cc2192058ab8dae3d306acbdaf2ce6574f@appspot.gserviceaccount.com>
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go