osmo-bsc_mgcp: Don't link against libosmo-netif

This fixes the following dpkg-shlibdeps warning:

Change-Id: I1eb079aa74a56b75e881b7abae0e5d9b4d7ae9c4
dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/osmo-bsc-mgcp/usr/bin/osmo-bsc_mgcp was not linked against libosmonetif.so.4 (it uses none of the library's symbols)

src/osmo-bsc_mgcp/Makefile.am

@@ -8,7 +8,6 @@ AM_CFLAGS = \
 	-Wall \
 	$(LIBOSMOCORE_CFLAGS) \
 	$(LIBOSMOVTY_CFLAGS) \
-	$(LIBOSMONETIF_CFLAGS) \
 	$(LIBBCG729_CFLAGS) \
 	$(COVERAGE_CFLAGS) \
 	$(NULL)
@@ -24,7 +23,6 @@ osmo_bsc_mgcp_SOURCES = \
 osmo_bsc_mgcp_LDADD = \
 	$(top_builddir)/src/libosmo-legacy-mgcp/libosmo-legacy-mgcp.la \
 	$(LIBOSMOCORE_LIBS) \
-	$(LIBOSMONETIF_LIBS) \
 	$(LIBOSMOVTY_LIBS) \
 	$(LIBBCG729_LIBS) \
 	$(LIBRARY_GSM) \