audiomixerbin: Remove elements when pad is released and it is not in playing state
audiomixerbin: Remove elements when pad is released and it is not in playing state

Change-Id: Iceecc596c044497f414b95cc86cd7e0acf68fa19

Kurento/kms-core,TribeMedia/kms-core,ESTOS/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,Kurento/kms-core,TribeMedia/kms-core,ESTOS/kms-core,Kurento/kms-core,ESTOS/kms-core,ESTOS/kms-core,KurentoLegacy/gst-kurento-plugins,shelsonjava/kms-core,shelsonjava/kms-core,TribeMedia/kms-core,KurentoLegacy/gst-kurento-plugins,Kurento/kms-core,TribeMedia/kms-core,KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins