fix display incoherence when pairing

The issue was caused by the fact that the list of
devices already discovered was systematically cleared
when a bond state changed event was received.
This fix removes the call to the clear list method.

Change-Id: I9e3644fd74353cb8b8eeda4357d998f68285dd11
Author: Christophe Bransiec <christophex.bransiec@intel.com>
Signed-off-by: Xiaokang Qin <xiaokang.qin@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 34349