Update index.yml

[chrisda]

Removed ms.subservice per build report

[learn-build-service-prod]

Learn Build status updates of commit 1ae4f78:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/docs-conceptual/index.yml	✅Succeeded	View (exchange-ps)

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 ec6f7a1:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/docs-conceptual/index.yml	✅Succeeded	View (exchange-ps)

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