Remove append-bottom-4 CSS class

What does this MR do?

This removes the .append-bottom-4 CSS class, no replacements were needed as this class wasn't used anywhere

#217418

Screenshots

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