Fix Tethys asset

When played on a device with MBDRC or on headphones, flaws in this
 asset become apparent: hiss throughout the sound, and positive
 true-peak on the first attack on the right channel.
This new version has reduced noise through substraction of the
 noise print at the end, and fadeout to silence. The asset is
 encoded with a 3dB headroom and a slight EQ.

Bug 11077919

Change-Id: I73ab91ca7118afd382e15a4673c332353294470e