Makefile.am: Don't link lots of openbsc / sgsn / ggsn internal .o files

this is probably a historic relict.  None of them should be used, and I
cannot see any actual use of them either.

The only non-library code that we link now is libosmo-gb (ns/bssgp),
which soon will be turned into a real library.

src/Makefile.am

@@ -65,19 +65,6 @@ pcu_LDADD = \
 	$(OPENBSC_DIR)/src/libgb/gprs_bssgp_bss.o \
 	$(OPENBSC_DIR)/src/libgb/gprs_bssgp_util.o \
 	$(OPENBSC_DIR)/src/libgb/gprs_ns_frgre.o \
-	$(OPENGGSN_DIR)/gtp/queue.o \
-	$(OPENGGSN_DIR)/gtp/lookupa.o \
-	$(OPENGGSN_DIR)/gtp/pdp.o \
-	$(OPENGGSN_DIR)/gtp/gtpie.o \
-	$(OPENGGSN_DIR)/gtp/gtp.o \
-	$(OPENBSC_DIR)/src/gprs/sgsn_libgtp.o \
-	$(OPENBSC_DIR)/src/gprs/gprs_sndcp.o \
-	$(OPENBSC_DIR)/src/gprs/crc24.o \
-	$(OPENBSC_DIR)/src/gprs/gprs_llc.o \
-	$(OPENBSC_DIR)/src/gprs/gprs_gmm.o \
-	$(OPENBSC_DIR)/src/gprs/gprs_sgsn.o \
-	$(OPENBSC_DIR)/src/libcommon/socket.o \
-	$(OPENBSC_DIR)/src/libcommon/debug.o \
 	$(LIBOSMOCORE_LIBS) \
 	$(LIBOSMOGSM_LIBS) \
 	$(COMMON_LA)