ASACORE-979 Fixed Timer Reentrancy error

The OnBusDisconnected method should not be calling EnableConcurrentCallbacks.
This was a pattern copied from the DeferredCallbacks::AlarmTriggered method
however calling EnableConcurrentCallbacks was not needed and resulted in the
Timer Reentrancy error when cleaning up the BusObjects. Resulting in warnings
that the user could not do anything about.

Change-Id: Ic41c21854bb42c05044cc9b9cc6289ccfeb1c077
Signed-off-by: George Nash <georgen@qce.qualcomm.com>
Merge "ASACORE-979 Fixed Timer Reentrancy error"