use new external libosmogb (part of libosmocore.git)

This removes the libgb (GPRS NS/BSSGP) code from the openbsc.git
repository and uses the new version from libosmocore.git instead.
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index db86b16..1ef0250 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -1,8 +1,9 @@
 INCLUDES = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
 AM_CFLAGS=-Wall -fno-strict-aliasing $(LIBOSMOCORE_CFLAGS) \
 	$(LIBOSMOGSM_CFLAGS) $(LIBOSMOVTY_CFLAGS) \
-	$(LIBOSMOABIS_CFLAGS) $(COVERAGE_CFLAGS)
-OSMO_LIBS = $(LIBOSMOCORE_LIBS) $(LIBOSMOGSM_LIBS) $(LIBOSMOVTY_LIBS)
+	$(LIBOSMOABIS_CFLAGS) $(LIBOSMOGB_CFLAGS) $(COVERAGE_CFLAGS)
+OSMO_LIBS = $(LIBOSMOCORE_LIBS) $(LIBOSMOGSM_LIBS) $(LIBOSMOVTY_LIBS) \
+	    $(LIBOSMOGB_LIBS)
 
 noinst_HEADERS = gprs_sndcp.h
 
@@ -13,13 +14,11 @@
 endif
 
 osmo_gbproxy_SOURCES = gb_proxy.c gb_proxy_main.c gb_proxy_vty.c
-osmo_gbproxy_LDADD = 	$(top_builddir)/src/libgb/libgb.a \
-			$(top_builddir)/src/libcommon/libcommon.a \
+osmo_gbproxy_LDADD = 	$(top_builddir)/src/libcommon/libcommon.a \
 			$(OSMO_LIBS)
 
 osmo_sgsn_SOURCES =	gprs_gmm.c gprs_sgsn.c gprs_sndcp.c gprs_sndcp_vty.c \
 			sgsn_main.c sgsn_vty.c sgsn_libgtp.c \
 			gprs_llc.c gprs_llc_vty.c crc24.c
-osmo_sgsn_LDADD = 	$(top_builddir)/src/libgb/libgb.a \
-			$(top_builddir)/src/libcommon/libcommon.a \
+osmo_sgsn_LDADD = 	$(top_builddir)/src/libcommon/libcommon.a \
 			-lgtp $(OSMO_LIBS)