audioflinger: fix pre processing effect leak

When a capture thread was closed, the effects attached to this thread
were left dangling and the associated effect chain destroyed.
When their last client was disconnected, the effects were not released
properly from the effect library because the destruction process could
not be completed without the effect being attached to a thread.

A similar problem prevented a RecordTrack to be properly released if
its client was destroyed after the capture thread.

The fix consists in allowing the effect or record track to be properly
released even if its parent thread cannot be promoted.

Also save any effect chain still present on a closed capture thread
in case a new client wants to reuse the effects on the same session later.

Bug: 17110064.
Change-Id: I5cd644daa357afd1f3548f9bcb28e6152d95fdb8