[release-branch.go1.12] cmd/go/internal/modload: remove erroneous test case

Commit e0cf3de987e6 of the vcs-test.golang.org/git/querytest repo
includes a go.mod file specifying path vcs-test.golang.org/git/querytest.git,
as does the latest commit. Since the repository also lacks v3 tags,
a query for "latest" with a v3 path should fail.

Due to a bug, that query does not fail as expected with Go 1.12.
However, we do not need to continue to test for buggy behavior that
was fixed in a subsequent release.

Updates #36489

Change-Id: I766390c962fc75ba98fad02831310d90abf3055f
Reviewed-on: https://go-review.googlesource.com/c/go/+/214281


Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>