Premium/Silver customers are able to find epics when trying to add an existing issue to an epic.

Summary

Premium/Silver customers are able to find epics when trying to add an existing issue to an epic. Child epics is an Ultimate feature. This ability to find epics for Premium customers adds confusion to our tier systems.

Steps to reproduce

1. On a Premium plan group create two epics: 'epic one' and epic two.
2. Go to epic one.
3. Under Issues block click Add -> Add an existing issue
4. Type in & symbol and a list of existing epics will show up in the suggestions list. Select epic two from the suggestions list.
5. Click Add primary button.

=> You'll get error Issue cannot be found.

Example Project

What is the current bug behavior?

Issue cannot be found.

What is the expected correct behavior?

Epics shouldn't show up in the list for non-Ultimate customers.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

If we move Nested epics to Premium tier as proposed in this issue, this will solve this bug.