Revert "cmd/go/internal/test: wrap os.Stdout always"

Revert "cmd/go/internal/test: wrap os.Stdout always"

This reverts CL 400877.

Reason for revert: broke TestScript/test_output_wait and the
regression test for #18153 on certain builders.

Fixes #52461.

Change-Id: I98627ce5e22088b0784be502c459480c41ba353a
Reviewed-on: https://go-review.googlesource.com/c/go/+/401494
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>