audioflinger: only exchange AUDIO_SOURCE_HOTWORD when using pre-kitkat audio-policy

Change-Id: I46bb3074484853682c75ddc417e77b6ae846136c
Revert "Fix decoder EOS handling"

 * This is causing carnage for apps and games which make assumptions
   about the (bad) behavior of EOS handling. While this patch makes
   it consistent across the board, let's stay bug-for-bug compatible.
 * L is going to break a lot of shit :(

This reverts commit ff9a42d3c4460714dcb963f1a9f22f06a8f7fc8d.

Change-Id: Iab33edf64f5ec02e4391713e2bd0630ea056b3fd