Remove "for internal use" text for SiteAndGroupProtectionLevel because it is not true

[hnguyen1218]

Submitted via Learn Editor.

[github-actions]

@lusassl-msft
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[learn-build-service-prod]

Learn Build status updates of commit d84658e:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/ExchangePowerShell/Set-Label.md	✅Succeeded	View (exchange-ps)

For more details, please refer to the build report.

[learn-build-service-prod]

Learn Build status updates of commit c85bfbe:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/ExchangePowerShell/Set-Label.md	✅Succeeded	View (exchange-ps)

For more details, please refer to the build report.