st-hal: Drop unnecessary COPY_HEADERS

COPY_HEADERS is rightfully and finally deprecated and dropped on R.
Nothing is currently using the sound_trigger interface.

Signed-off-by: Marijn Suijten <marijns95@gmail.com>
Change-Id: I375c0273cc78ee6b9cbd982aafd0100cff2e6170
diff --git a/Android.mk b/Android.mk
index c31ffdc..e21555d 100644
--- a/Android.mk
+++ b/Android.mk
@@ -112,9 +112,6 @@
 LOCAL_VENDOR_MODULE := true
 LOCAL_MULTILIB := $(AUDIOSERVER_MULTILIB)
 
-LOCAL_COPY_HEADERS_TO   := mm-audio/sound_trigger
-LOCAL_COPY_HEADERS      := sound_trigger_prop_intf.h
-
 include $(BUILD_SHARED_LIBRARY)
 
 #