Reimplement exchange prep_sync_lists ourselves

As explained in earlier commits, the exchange EWS operations only
allow us to fetch changes from the client. It is impossible to use
the syncstate infra to push changes from client to server.

So with this commit we fallback to the manaual generation of the
sync lists - by first fethcing all the items, and then looking that
up against the items list from the last sync.

It works. :)
Remove code added for tracking server sync state

As explained in previous commit comments we cannot use Exchange
server side sync state completely for our bi-dirctional sync
use case. In view of the fact that we have reimplemented this
manually, let's get rid of the stuff that was added for supporting
the Exchange sync folder stuff.