cmd/doc: print bugs with -all flag

cmd/doc: print bugs with -all flag

Includes cleanup and deduplication.

fixes: #33970

Change-Id: I7e84b3e5c8fb9c560cf0a1f8b7cbb7a6977666aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/511935
Reviewed-by: Rob Pike <r@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>