[Bluetooth]: Remove the usage of /proc completely

This patch removes all relics of the /proc usage from the Bluetooth
subsystem core and its upper layers. All the previous information are
now available via /sys/class/bluetooth through appropriate functions.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David S. Miller <davem@davemloft.net>