$VM1 = Get-AzureVM -ServiceName “cloudservice” -Name “vmname”
Set-AzureVMExtension -VM $VM1 –Uninstall -ReferenceName “VMSnapshot” -ExtensionName “VMSnapshot” -Publisher “Microsoft.Azure.RecoveryServices” -Version “1.0” | Update-AzureVM

My Previous post talks about how to remove BGINFO extension from a VM when migrating VM from ASM to ARM