Hide Mark as draft button in a merged MR even on mobile

What does this MR do?

Hides "Mark as draft" button in a merged MR even on mobile.

Screenshots (strongly suggested)

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• [n/a] Merge request performance guidelines
• Style 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

Related to #282506 (closed)