.github: delete archived issue templates

.github: delete archived issue templates

We can get the previous templates back from version control if needed.
Delete these unused copies to avoid confusion.

For #63970.

Change-Id: I44e54da06e259239745f4a493de1dae94cca3755
Reviewed-on: https://go-review.googlesource.com/c/go/+/544536
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>