Remove deprecation warning for split up NGINX Config/Unit roles

[alessfg]

Proposed changes

Remove the deprecation warning in the README detailing the advent of the NGINX Core Ansible collection and the subsequent splitting from this role of the Ansible NGINX Config role and the Ansible NGINX Unit role.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have added Molecule tests that prove my fix is effective or that my feature works
• I have checked that any relevant Molecule tests pass after adding my changes
• I have updated any relevant documentation (defaults/main/*.yml, README.md and CHANGELOG.md)