Fix memory leak when filtering commands in insertCommand_l()

When AudioPolicyService::AudioCommandThread::insertCommand_l filters
a command from the queue, the AudioCommand* is removed from the
vector mAudioCommands by calling mAudioCommands.removeAt(). This will
destroy the pointer and compact the vector, but not delete the
AudioCommand object.

This patch adds code to delete a filtered out AudioCommand and its
data object mParam. However, mParam was void* and deleting a void
pointer is undefined behavior according to the C++
standard. Therefore, the data classes are modified to inherit
from an abstract base class with a virtual destructor.

The deletion of non-filtered commands in
AudioPolicyService::AudioCommandThread::threadLoop() was already
correct, as each case casts mParam to the proper type before
deleting.

This also fixes AOSP issue 36370.

Change-Id: I2b63838aff3608132aa496f964a929f78c4b6267