docs(deployment): remove obsolete "serverless" section (#1478)
docs(deployment): remove obsolete "serverless" section (#1478)

The _serverless_ section had a broken link since the specific _serverless_ page was removed [here](https://github.com/probot/probot/commit/c612fc903de291a620867713c7fc774242937795#). Furthermore, it feels redundant to keep this section now that we have a section about _serverless functions_ in this _deployment_ page.

* Update deployment.md

Co-authored-by: Gregor Martynus <c75b6165e9a4db95682128147fce435572bf5c5b@users.noreply.github.com>
probot/probot,probot/probot,probot/probot