Remove `-o` documentation from SSH key generation

What does this MR do?

Removes -o option from the ssh-keygen documentation.

ssh-keygen -o does not exist in the ssh-keygen manpages, nor is the -o option sourced in the blog referenced in the existing doc.

Closes #33492 (closed).

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content