Update cross-tenant-mailbox-migration.md

[msbemba]

trafficstars

Removed information on domain sharing as it is removed from the roadmap (67161 )

Fixes https://github.com/MicrosoftDocs/microsoft-365-docs-pr/issues/23620

[msbemba]

@JohanFreelancer9 Please copy review

[learn-build-service-prod[bot]]

Learn Build status updates of commit 3d862cd:

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[yogkumgit]

@kelleyvice-msft Please merge this PR. Thanks

[yogkumgit]

@kelleyvice-msft Gentle reminder.