Remove close method from RequestProcessor

Wit new implementation of RequestProcessor, transactions are better
managed, and their closure is assured by the commit. Letting the user
interfere in transaction management can make the application very
instable.
So, remove close method from NetworkTransactionService interface.

JIRA: TRNSPRTPCE-727
Signed-off-by: Gilles Thouenon <gilles.thouenon@orange.com>
Change-Id: I9b384c729d105795d0047d51149f9bf9342ce298