Remove A2DP connect logic from settingslib

A2dpProfile will disconnect current device when receive connect event
and max connectable device is one. Ideally we shouldn't have any
bluetooth code in settingslib. The corresponding logic is moved to
the Bluetooth A2dpService.

Bug: 111812003
Test: 1. Developer options > Maxium connected Bluetooth device > 1.
      2. Connected 2 BT Headset respectively

Change-Id: I298c39942756523b8a2b34a4104bcd247d2455eb