The changes introduced to resolve the EZP-29938 Story provided CoreInstaller, however due to optional (BC-safe) dependency on DoctrineSchemaBundle, it hasn't been explicitly defined in the Dependency Injection Container. Thus, while it resolved BC on extending CleanInstaller perfectly, it didn't allow for a clean upgrade.

We need to provide:

• explicit FQCN-named definition of CoreInstaller and its removal if Bundle is not active (with deprecation message),
• for consistency FQCN-named definition of DbBasedInstaller.