Update onboard-windows-multi-session-device.md

[cmckitterick]

Added clarification that customers do not need to manually offboard session hosts to address customer confusion.

[learn-build-service-prod]

Learn Build status updates of commit d3a07c1:

✅ Validation status: passed

File	Status	Preview URL	Details
defender-endpoint/onboard-windows-multi-session-device.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[denisebmsft]

Thank you @cmckitterick

[learn-build-service-prod]

Learn Build status updates of commit c2e03cb:

✅ Validation status: passed

File	Status	Preview URL	Details
defender-endpoint/onboard-windows-multi-session-device.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit e3d7c19:

✅ Validation status: passed

File	Status	Preview URL	Details
defender-endpoint/onboard-windows-multi-session-device.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel