osmo-hnbgw: Avoid useless linking to libosmogsm and libsctp

This fixes the following dpkg-shlibeps warnings:

Change-Id: Ic6a645a93406670d58eb5edf5f2f2e1266168c92
dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/osmo-hnbgw/usr/bin/osmo-hnbgw was not linked against libosmogsm.so.8 (it uses none of the library's symbols)
dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/osmo-hnbgw/usr/bin/osmo-hnbgw was not linked against libsctp.so.1 (it uses none of the library's symbols)
diff --git a/src/Makefile.am b/src/Makefile.am
index d815394..a45b70b 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -45,7 +45,6 @@
 AM_CFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include \
 	    $(OSMOCORE_CFLAGS) $(OSMOVTY_CFLAGS) $(OSMOGSM_CFLAGS) \
 	    $(OSMONETIF_CFLAGS) $(ASN1C_CFLAGS) $(OSMOSIGTRAN_CFLAGS)
-COMMON_LDADD = -lsctp
 
 # build the shared RANAP library
 #
@@ -68,7 +67,7 @@
 		     hnbgw_vty.c \
 		     context_map.c hnbgw_cn.c
 
-osmo_hnbgw_LDADD = $(OSMOCORE_LIBS) $(OSMOVTY_LIBS) $(OSMOGSM_LIBS) \
+osmo_hnbgw_LDADD = $(OSMOCORE_LIBS) $(OSMOVTY_LIBS) \
 		   $(ASN1C_LIBS) $(OSMOSIGTRAN_LIBS) $(COMMON_LDADD) \
 		   $(OSMONETIF_LIBS) \
 		   hnbap/libosmo-asn1-hnbap.a rua/libosmo-asn1-rua.a \