Remove .exclusive from Epic positioning spec

What does this MR do?

Resolves master:broken with the recommendation at #247120 (comment 409990345).

The spec is showing that that epic3's relative position is not updated which may lead to inconsistent ordering between epic_issue2 and epic3. For now this seems acceptable until further investigation in #247120 (closed) occurs.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• [-] 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.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done