The EzSystems\PlatformInstallerBundle\Installer\CleanInstaller needs to be dropped and code around installers needs to be cleaned up before proceeding with EZP-30624.

Due to bundle-optional dependency on the new SchemaBuilder there was no possibility to provide forward compatibility layer, so there will be changes required for 3rd party packages or projects implementing custom installers when upgrading to eZ Platform 3.0.