Drop deprecated or unmaintained generators.

[mshima]

Overview of the feature request

To be dropped

• [ ] add
• [ ] init
• [ ] upgrade-config

Consider to drop:

• [ ] aws
• [ ] azure-app-service
• [ ] azure-spring-cloud
• [ ] cloudfoundry
• [ ] gae
• [ ] openshift
• [ ] openapi-client

Consider to implement as a command or option:

• [ ] info
• [ ] export-jdl
• [ ] page
• [ ] spring-controller
• [ ] spring-service

Motivation for or Use Case

Improve maintainability and developer experience

Related issues or PR

• [ ] Checking this box is mandatory (this is just to show you read everything)