Simplify Requests::Service::Receive

In anchient times users would set up their service hooks on GitHub manually. We then created the repository and owner instances on our side based on the incoming request data.

This is now outdated. We require people to set the service hook on our side, and the repository and owner records will be created at user sync time.

How to deploy: bump travis-core in gatekeeper, deploy gatekeeper to production

For the `github_guid` to be set this also needs to be merged and bumped in gatekeeper: https://github.com/travis-ci/travis-sidekiqs/pull/3