Remove EE specific lines from spec/lib/system_check/app/git_user_default_ssh_config_check_spec.rb

What does this MR do?

Removes not needed lines from spec/lib/system_check/app/git_user_default_ssh_config_check_spec.rb in order to achieve unified codebase.

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

Closes #6495 (closed)