Hearing Aid: fix logic in connect and disconnect

* Hearing Aid Service reads the HiSyncId map and connect to the given
device and also the other side device (if any) at the same time. Before
connecting, the Hearing Aid Service disconnects devices from other pair.
* Simplify the logic in connect and disconnect to handle devices with
same HiSyncId.

Bug: 69623109
Test: unit test
Change-Id: Ib6e966e2aa51c991d89c9993f685aa15c039b89b
(cherry picked from commit 8b683ddb)