stereo: remove plugin which has been merged into audiofx in -good

gstreamer/gst-plugins-bad#457
6 jobs for audiofx-move in 29 minutes and 4 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #69581
gst indent

00:00:14

passed #69580
manifest

00:00:39

 
  Build
passed #69582
build fedora x86_64

00:04:41

 
  Test
passed #69583
check fedora

00:14:29

 
  Full Builds
passed #69584
build android arm64 api28

00:05:25

passed #69585
build cerbero fedora x86_64

00:09:13