Sourcegraph: Remove DigitalOcean 1-click app

[dadlerj]

We should take it down entirely ASAP given we're not investing in updating the docs — it still shows instructions for Sourcegraph 3.4! https://marketplace.digitalocean.com/apps/sourcegraph

[dadlerj]

Duplicate of https://github.com/sourcegraph/sourcegraph/issues/6666

[unknwon]

I'm closing this one... it seems identical to #6666 and we already have discussions on that thread.

[dadlerj]

Oops, I thought by marking as a duplicate, this would get auto-closed... Thanks!