Remove dup header rules.

This fixes the build warning:
build/core/copy_headers.mk:15: warning: overriding commands for target
`out/host/linux-x86/obj/include/libexpat/expat.h'
build/core/copy_headers.mk:15: warning: ignoring old commands for target
`out/host/linux-x86/obj/include/libexpat/expat.h'
build/core/copy_headers.mk:15: warning: overriding commands for target
`out/host/linux-x86/obj/include/libexpat/expat_external.h'
build/core/copy_headers.mk:15: warning: ignoring old commands for target
`out/host/linux-x86/obj/include/libexpat/expat_external.h'

Change-Id: Ifa754483a4aa066f2d5f03e64b9a95e1643c0390
diff --git a/Android.mk b/Android.mk
index 0d8a350..e62a069 100644
--- a/Android.mk
+++ b/Android.mk
@@ -33,8 +33,6 @@
 
 LOCAL_MODULE:= libexpat
 LOCAL_MODULE_TAGS := optional
-LOCAL_COPY_HEADERS_TO := $(common_COPY_HEADERS_TO)
-LOCAL_COPY_HEADERS := $(common_COPY_HEADERS)
 
 include $(BUILD_HOST_STATIC_LIBRARY)
 
@@ -95,4 +93,3 @@
 LOCAL_COPY_HEADERS := $(common_COPY_HEADERS)
 
 include $(BUILD_SHARED_LIBRARY)
-