Bluetooth: hidp: remove old session-management

We have the full new session-management now available so lets switch over
and remove all the old code. Few semantics changed, so we need to adjust
the sock.c callers a bit. But this mostly simplifies the logic.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>