Remove beta check for project subscriptions

What does this MR do?

Changes the beta_feature_available check to feature_available. This feature was never supposed to be in a beta state.

Does this MR meet the acceptance criteria?

Conformity

• N/A Changelog entry
• N/A Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• N/A Database guides
• N/A Separation of EE specific content