runtime: don't duplicate reraised panic values in printpanics

runtime: don't duplicate reraised panic values in printpanics

Change the output printed when crashing with a reraised panic value
to not duplicate that value.

Changes output of panicking with "PANIC", recovering, and reraising
from:

  panic: PANIC [recovered]
    panic: PANIC

to:

  panic: PANIC [recovered, reraised]

Fixes #71517

Change-Id: Id59938c4ea0df555b851ffc650fe6f94c0845499
Reviewed-on: https://go-review.googlesource.com/c/go/+/645916
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>