Review and remove some parts of API DevOps section

The section https://access.redhat.com/documentation/en-us/red_hat_3scale/2.saas/html/api_devops/ (and its on-prem variants) contains outdated information, which is not supported anymore (like Chef deployment, or some examples of the nginx configuration).

This section should be carefully reviewed, and probably we only need to keep the Troubleshooting section, which also needs to be reviewed to see if it needs any updates.