We are having a hard time deciding the exact semantics
of the Err field, and we need to ship the beta.
So revert the Err field change; it can wait for Go 1.20.
For #51115.
This reverts CL 396215.
Change-Id: I7719386567d3da10a614058a11f19dbccf304b4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/410133
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>
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