x/build/app/appengine: hide and stop testing release-branch.go1.9

[dmitshur]

https://build.golang.org/ currently displays:

• Sub-repositories at tip
• Sub-repositories at release-branch.go1.11
• Sub-repositories at release-branch.go1.10
• Sub-repositories at release-branch.go1.9

Per policy, we support only current and previous releases. Go 1.11 is out now, so 1.9 should be dropped.

[gopherbot]

Change https://golang.org/cl/133895 mentions this issue: app/appengine: hide and stop testing release-branch.go1.9

[dmitshur]

Still need to redeploy the dashboard for this change to take effect. Reopening for tracking that.

[dmitshur]

Deployed and resolved. https://build.golang.org/ has only 1.11 and 1.10 now.