The Azure Disk Encryption engineering team has deprecated the Linux security extension "Microsoft.OSTCExtension.AzureDiskEncryptionForLinux". This extension was published for Azure disk encryption preview release. You should not use the preview version of the extension in your testing or production deployment.
For deployment scenarios like Azure Resource Manager (ARM), where you have a need to deploy Azure disk encryption extension for Linux VM to enable encryption on your Linux IaaS VM, you must use the Azure disk encryption production supported extension "Microsoft.Azure.Security.AzureDiskEncryptionForLinux".
For deployment scenarios using Azure PowerShell SDK, you must use the latest version of the Azure PowerShell SDK. Download the latest version of Azure PowerShell release, which deploys the latest supported version of Azure disk encryption extension "Microsoft.Azure.Security.AzureDiskEncryptionForLinux"
For more details on Azure Disk Encryption solution and supported deployment scenarios, refer to the ADE whitepaper located at https://docs.microsoft.com/en-us/azure/security/azure-security-disk-encryption