Bluetooth: hidp: remove unused session->state field

This field is always BT_CONNECTED. Remove it and set it to BT_CONNECTED in
hidp_copy_session() unconditionally.

Also note that this field is totally bogus. Userspace can query an
hidp-session for its state. However, whenever user-space queries us, this
field should be BT_CONNECTED. If it wasn't BT_CONNECTED, then we would be
currently cleaning up the session and the session itself would exit in the
next few milliseconds. Hence, there is no reason to let user-space know
that the session will exit now if they cannot make _any_ use of that.

Thus, remove the field and let user-space think that a session is always
BT_CONNECTED as long as they can query it.

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>