Remove unused managementSubnetPrefix ARM param

samples/manage/azure-sql-db-managed-instance/attach-jumpbox/attachJumpbox.ps1

@@ -178,7 +178,6 @@ If($false -eq $subnets.Contains($managementSubnetName))
     SetVirtualNetwork $virtualNetwork
     Write-Host "Added subnet into VNet." -ForegroundColor Green
 } else {
-    $managementSubnetPrefix = 'N/A'
     Write-Host "The subnet already exists in the VNet." -ForegroundColor Green
 }
 
@@ -189,7 +188,6 @@ Write-Host "Starting deployment..."
 
 $templateParameters = @{
     virtualNetworkName = $virtualNetworkName
-    managementSubnetPrefix  = $managementSubnetPrefix
     managementSubnetName  = $managementSubnetName
     virtualMachineName  = $virtualMachineName
     administratorLogin  = $administratorLogin

samples/manage/azure-sql-db-managed-instance/attach-jumpbox/azuredeploy.json

@@ -15,13 +15,6 @@
                 "description": "Enter virtual network name. If you leave this field blank name will be created by the template."
             }
         },
-        "managementSubnetPrefix": {
-            "type": "string",
-            "defaultValue":"THIS IS NOT USED",
-            "metadata": {
-                "description": "Enter management subnet address prefix."
-            }
-        },
         "administratorLogin": {
             "type": "string",
             "metadata": {