Revert "removing system data and x-ms-azure extension from tracked re…

…source (because making changes in the tracked resource will involove dsMianDev repo changes)"

This reverts commit e330db6.
SystemData is required to be in trackedResource

specification/datamigration/resource-manager/Microsoft.DataMigration/preview/2021-10-30-preview/sqlmigration.json

@@ -1435,8 +1435,13 @@
         "type": {
           "type": "string",
           "readOnly": true
+        },
+        "systemData": {
+          "$ref": "#/definitions/SystemData",
+          "readOnly": true
         }
-      }
+      },
+      "x-ms-azure-resource": true
     },
     "SqlMigrationService": {
       "description": "A SQL Migration Service.",