Azure Web App deployment targets have been deprecated in Octopus 3.1, and have been replaced by the 'Deploy an Azure Web App Step'.
Don't worry - you can migrate your Azure Targets to use the equivalent Azure Steps by following this guide.
Octopus Deploy supports automated deployment of Azure Web Apps (formerly known as Azure Web Sites).
Azure Web App Deployment Target
In Environments you can create Azure Web App Deployment Targets.
For more information on deploying Azure Web Apps with Octopus using this deployment target please refer to deploying a package to an Azure Web App. The same options and process is used by the deployment target and the deployment step.