runtime: cleanup crashstack code
This patch removes redundant guards for the crash stack feature, as all
supported Go architectures now have a crash stack implementation.
Change-Id: I7ffb61c57955778d687073418130b2aaab0ff183
GitHub-Last-Rev:
6ff56d6420093ee8f95c75019557dc8bcec32ed7
GitHub-Pull-Request: golang/go#67202
Reviewed-on: https://go-review.googlesource.com/c/go/+/583416
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Mauri de Souza Meneguzzo <mauri870@gmail.com>