Move osmo_gsup_messages.[ch] to libosmocore

This requires the corresponding commit in libosmocore.
diff --git a/openbsc/tests/gprs/Makefile.am b/openbsc/tests/gprs/Makefile.am
index 633c362..902313f 100644
--- a/openbsc/tests/gprs/Makefile.am
+++ b/openbsc/tests/gprs/Makefile.am
@@ -5,7 +5,6 @@
 
 noinst_PROGRAMS = gprs_test
 
-gprs_test_SOURCES = gprs_test.c $(top_srcdir)/src/gprs/gprs_utils.c \
-		$(top_srcdir)/src/gprs/gprs_gsup_messages.c
+gprs_test_SOURCES = gprs_test.c $(top_srcdir)/src/gprs/gprs_utils.c
 
 gprs_test_LDADD = $(LIBOSMOCORE_LIBS) $(LIBOSMOGSM_LIBS)