Reverts commit 81c16273c543822fa8b87522cb1146a7859edd7a in the mpd repo

--- ../SlesOutputPlugin.cxx.orig	2020-04-03 22:18:11.070009046 +0200
+++ ./src/output/plugins/sles/SlesOutputPlugin.cxx	2020-04-03 22:18:58.189898556 +0200
@@ -28,7 +28,6 @@
 #include "util/Macros.hxx"
 #include "util/Domain.hxx"
 #include "system/ByteOrder.hxx"
-#include "mixer/MixerList.hxx"
 #include "Log.hxx"
 
 #include <SLES/OpenSLES.h>
@@ -413,5 +412,5 @@
 	"sles",
 	sles_test_default_device,
 	SlesOutput::Create,
-	&android_mixer_plugin,
+	nullptr,
 };