MODE-2343 Removed the EVENT related statistics from the JcrObservationManager and fixed the cleanup code required when a session is terminated (either via logout or repository shutdown)

Fixing the cleanup required by `session.logout` exposed another "interesting" issue: internal sessions (created via `session.spawnSession`) should never be logged out because doing do would invalidate their context (and therefore the context of the owner session).
Why did you remove the code to log out of the `restoreSession`?