Remove FF_AUTO_MAX_PROCS flag

What does this MR do?

Remove FF_AUTO_MAX_PROCS flag.

The flag has been enabled in production for a couple of months now gitlab-com/gl-infra/k8s-workloads/gitlab-com!3430 (merged), so we can remove this from the code now.

TODO

• Feature flag
  • Added feature flag:
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines

Closes #1096 (closed)