cmd/internal/objabi: remove -V=goexperiment internal special case
This special case was added in CL 310171 for test/run.go use, as the
comment still says, but run.go (cmd/internal/testdir/testdir_test.go
by now) stopped using this in CL 310732. There don't seem to be any
other internal or external uses of this special case, so delete it.
Doing this kind of a cleanup can become harder as more time passes,
so try it as early as now and see how it goes.
Change-Id: Ib52aac51ef05166f7349cfc7d63b860a8ece7ec0
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/720620
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Michael Matloob <matloob@google.com> Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>