move OAP messages implementations to libosmocore

This corresponds to change-id If5099e60681a215e798b6675f21813f26769c253 in
libosmocore, which is now required to build openbsc.

Related: OS#1592
Change-Id: I2f06aaa6eb54eafa860cfed8e72e41d82ff1c4cf
diff --git a/openbsc/tests/oap/oap_test.c b/openbsc/tests/oap/oap_test.c
index d200ed2..68542fd 100644
--- a/openbsc/tests/oap/oap_test.c
+++ b/openbsc/tests/oap/oap_test.c
@@ -19,11 +19,10 @@
  */
 
 #include <osmocom/core/application.h>
+#include <osmocom/gsm/oap.h>
 
 #include <openbsc/debug.h>
-
 #include <openbsc/oap.h>
-#include <openbsc/oap_messages.h>
 
 #include <stdio.h>
 #include <string.h>