don't re-implement osmo_talloc_replace_string()

osmo_talloc_replace_string() was introducd into libosmocore in 2014, see
commit f3c7e85d05f7b2b7bf093162b776f71b2bc6420d

There's no reason for us to re-implement this as bsc_replace_string
here.

Change-Id: I6d2fcaabbc74730f6f491a2b2d5c784ccafc6602
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
index bb0f4c4..c12b29f 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
@@ -139,7 +139,7 @@
 
 void bsc_nat_set_msc_ip(struct bsc_nat *nat, const char *ip)
 {
-	bsc_replace_string(nat, &nat->main_dest->ip, ip);
+	osmo_talloc_replace_string(nat, &nat->main_dest->ip, ip);
 }
 
 struct bsc_connection *bsc_connection_alloc(struct bsc_nat *nat)