Refactor out empty constant

What does this MR do?

Write out Clusters::Cluster::PROJECT_ONLY_APPLICATIONS constant

Conformity

• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.