audio: Drop LOCAL_COPY_HEADERS usage

LOCAL_COPY_HEADERS is deprecated, so remove all its usages
to avoid build warnings.

Change-Id: I4c52508e9109c5f448653fd5613a8991d28bbb2e
(cherry picked from commit 9abdcc75b4d8379e4b2d30a1068526e9dcae9425)
diff --git a/hal/Android.mk b/hal/Android.mk
index 4651e19..5f1e92a 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -383,8 +383,7 @@
 LOCAL_CFLAGS += -D_GNU_SOURCE
 LOCAL_CFLAGS += -Wall -Werror
 
-LOCAL_COPY_HEADERS_TO   := mm-audio
-LOCAL_COPY_HEADERS      := audio_extn/audio_defs.h
+LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)
 
 ifeq ($(strip $(AUDIO_FEATURE_ENABLED_GCOV)),true)
     LOCAL_CFLAGS += --coverage -fprofile-arcs -ftest-coverage