dbusoob: Simplify DBusConnection object handling
dbusoob: Simplify DBusConnection object handling

This patch removes local reference to DBusConnection object and uses
btd_get_dbus_connection() call wherever such object is needed instead.

Pointer returned by this call is guaranteed to be valid for entire
bluetoothd lifetime and thus do not need to be refcounted.

silent-snowman/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,ComputeCycles/bluez,ComputeCycles/bluez,mapfau/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,pkarasev3/bluez,mapfau/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,silent-snowman/bluez,pkarasev3/bluez,silent-snowman/bluez,silent-snowman/bluez