doc: delete commented out staging section

The staging section was commented out because that environment is not
supported. It's still visible when viewing the .md file in its raw form
and has proven to cause confusion. Since we can easily get it back from
history if/when it becomes needed again, hide it better by deleting it.

Change-Id: Ifb227d3238d88a9d1c6be58dd95e2b7829b85315
Reviewed-on: https://go-review.googlesource.com/c/build/+/463575
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

doc/deployment.md

@@ -21,23 +21,6 @@ $ gcloud auth configure-docker
 
 Install the App Engine Go SDK: [instructions](https://cloud.google.com/sdk/docs/quickstart-debian-ubuntu)
 
-<!--
-### Staging
-
-First, configure `gcloud`:
-
-```sh
-$ gcloud config set project go-dashboard-dev
-$ gcloud container clusters get-credentials --zone=us-central1-f go
-```
-
-Then to deploy, run:
-
-```sh
-$ make deploy-staging
-```
--->
-
 ### Prod
 
 First, configure `gcloud`: