Refactor Plan QA tests to use Login Flow

What does this MR do?

Refactor Plan QA tests to use Login Flow and by doing so reduces the code base in 31 lines.

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