Remove api-review workflow

[hdamker]

Problem description

The api-review reusable workflow and its supporting code are dead. The only consumer was camaraproject/ReleaseManagement, which no longer hosts release review issues. The Validation Framework (camaraproject/ReleaseManagement#448) fully covers these checks.

Possible evolution

Remove the following at any time:

• .github/workflows/api-review-reusable.yml
• scripts/api_review_validator_v0_6.py
• api-review/ directory
• README references to the api-review workflow
• Caller workflow in camaraproject/ReleaseManagement (.github/workflows/api-review-trigger.yml)

[hdamker]

The caller workflow in camaraproject/ReleaseManagement (.github/workflows/api-review-trigger.yml) can be removed independently, ahead of the tooling-side cleanup tracked here.