Remove var_call_ref from database.

[talavis]

Describe the pull request:

• [ ] Bug fix
• [X] Functional change
• [ ] New feature
• [ ] Code cleanup
• [ ] Build system change
• [ ] Documentation change
• [ ] Language translation

Pull request long description:

Remove var_call_ref from database and consider the value in data.reference_sets.reference_build to be its replacement.