Remove deprecated/unsupported features, methods and interfaces

This includes:

• bootstrap initialization logic (see also HCM-83)
  • pretty much everything under org.onehippo.repository.bootstrap package (few exceptions)
  • interface InitializationProcessor (2x)
  • interface ReferenceWorkspace
• deprecated Hippo JCR extensions/methods, like in HippoSession
• support for XA transactions/sessions (never used, but cannot be done right now, see: REPO-2059)
• package org.onehippo.repository.embeddedrmi (REPO-276), never used
• deprecated interface CronExpression (not used)
• deprecated interface org.hippoecm.repository.ext.DaemonModule (unused)
• deprecated interface org.onehippo.repository.api.ContentResourceLoader (unused)
• deprecated interface org.onehippo.repository.events.Persisted (unused)
• connector: JCR decorators in package org.hippoecm.repository.decorating (not child packages though)
  • these are only extended and used by the decorators in org.hippoecm.repository.impl
  • the connector decorators logic will be 'pushed down' and removed from there