frameworks/base: libexpat now exports its headers.

Change-Id: Iaba3d57db18ebdd89e4a993436e9bf844722ff87
diff --git a/tools/aapt/StringPool.h b/tools/aapt/StringPool.h
index dbe8c85..be843a8 100644
--- a/tools/aapt/StringPool.h
+++ b/tools/aapt/StringPool.h
@@ -20,7 +20,7 @@
 #include <ctype.h>
 #include <errno.h>
 
-#include <libexpat/expat.h>
+#include <expat.h>
 
 using namespace android;