Bluetooth-OPP: Remove OBEX session cleanup from OPP Service

OBEX session cleanup should be initiated from corresponding session
instead of OPP Service. Otherwise, during batch transfer if next file
in the batch starts before updating the previous transfer that will
lead to mismatch in status. This will cause UI progress bar stall
and transfer failure.

CRs-Fixed: 756084
Change-Id: Ibfa787396fe5f4f5b678ebcb4bdd36cb6641a161