Remove stale link to retired DMA documentation

The Data Migration Assistant (DMA) documentation was retired and removed from
the repository (commit a9ce55d). Removed the broken reference to
docs/dma/dma-overview.md which no longer exists.

The link was originally pointing to retired content that has been removed.

Author: VanMSFT

azure-sql/migration-guides/virtual-machines/oracle-to-sql-on-azure-vm-guide.md

@@ -349,4 +349,3 @@ The Data SQL Engineering team developed these resources. This team's core charte
 - [Best practices to cost and size workloads migrated to Azure](/azure/cloud-adoption-framework/migrate/azure-best-practices/migrate-best-practices-costs)
 - [Change the license model for a SQL virtual machine in Azure](../../virtual-machines/windows/licensing-model-azure-hybrid-benefit-ahb-change.md)
 - [Extend support for SQL Server with Azure](../../virtual-machines/windows/sql-server-extend-end-of-support.md)
-- [Data Access Migration Toolkit Preview](../../../docs/dma/dma-overview.md)