chore: Remove Dependabot

[alessfg]

Proposed changes

Now that Renovate is up and running, there no longer is a need for Dependabot.

Checklist

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

• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added Molecule tests that prove my fix is effective or that my feature works.
• If applicable, 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).