Bluetooth: Cleaning up sap service object to avoid serviceRecord leaks

A case where script is running to do BT ON/OFF 2000 times. Sap service
class object is leaked while turning OFF BT, when it is referenced
(Directly OR Indirectly due to its member variables). So Garbage
Collector doesn't collect class object which is referenced. Setting
NULL for service class object & service connection, while cleaning up
those variable to mark as weak reference. Any objects memory is
immediately claimed by GC, which are marked as weak reference.

Change-Id: I905d1e542c159c8f9addcb8491aee900697c9006
CRs-Fixed: 591180