Stop synth when tts client dies.

There was code to stop synthesis when a tts client died
but it was commented out in a seemingly unrelated CL,
possibly in error. Restore the code, now synthesis stops
as expected when the calling app dies.

Bug: 78187631
Test: Start playing a long body of text with the test app,
      kill it is adb shell am force-stop. With this change,
      the tts playout no longer continues.

Change-Id: I647ddcc46416ca33db4ad0fdbfca1fb5e88924a1