CEC: Remove system audio on hotplug

System audio was not being immediately removed by polling mechanism
mechanism but was being checked three times in order to avoid accidental
polling failure. This came with a side effect of the system audio
not removed instantly even when the device is physically removed.

This CL relies on hotplug event to tell whether the device removal
should be done right away or has to wait for 3 polling intervals.

Bug: 20133405
Change-Id: I9dbd7a8b9e424d523d0c22e4cac19b341461b71e