Remove delay received from audio layer for A2DP state changes

Due to changes in the audio layer, the
setBluetoothA2dpDeviceConnectionState() function now returns a
delay of 0 on a state change from disconnecting to disconnected.
After a discussion with the audio team, the delay returned by
this function isn't actually relevant to the A2DP state machine
so instead remove the dependency on the delay returned.

Bug: 37906688
Test: Disconnect from headset multiple times and see that it is
      not stuck disconnecting.

Change-Id: I108cc5230a571edbd26fcb1f985a0b14cb7123b6