Revert "Audio V4: Split system and vendor Audio.h"

This reverts commit f8ad7f85e9891b2614338330c75ae9e946fccc5a.

Reason for revert: Breaks the build of multiple devices

Change-Id: I24f17a0fa0c7ba171c4a3639f890e7f4e42f6b1e
diff --git a/media/libeffects/downmix/Android.mk b/media/libeffects/downmix/Android.mk
index f32b7e7..a5fbf14 100644
--- a/media/libeffects/downmix/Android.mk
+++ b/media/libeffects/downmix/Android.mk
@@ -17,14 +17,12 @@
 LOCAL_MODULE_RELATIVE_PATH := soundfx
 
 LOCAL_C_INCLUDES := \
+	$(call include-path-for, audio-effects) \
 	$(call include-path-for, audio-utils)
 
 #-DBUILD_FLOAT
 LOCAL_CFLAGS += -fvisibility=hidden
 LOCAL_CFLAGS += -Wall -Werror
 
-LOCAL_HEADER_LIBRARIES += \
-    libhardware_headers \
-    android.hardware.audio.effect.legacy@2.0 \
-
+LOCAL_HEADER_LIBRARIES += libhardware_headers
 include $(BUILD_SHARED_LIBRARY)