Removal of E2Session and use of the RNIB instead

It is suggested to use the same entities.NodebInfo we currently use instead of using a new structure under a different key.

The setup response handlers (x2/endc positive and negative) shall retrieve the entry from the rNib using the value of MEID (and not the xaction).

The prehandlers (as of now) shall attempt to retrieve an entry from the rNib before saving an entry in the rNib.

Need to replace the use of the E2Session in the UT with rnib mock.

ExecuteSetup() puts information in the E2Session - no need (Idan & Irina are going to take care of the prehandlers setup response handlers)