[nat] Remove the imsi allow option on the nat level.

For now we have:
1.) bsc imsi deny to deny at the BSC level
2.) bsc imsi allow to allow a SIM at the BSC level
3.) nat imsi deny to deny at the global level
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index e16910e..8e4261b 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -228,16 +228,7 @@
 		}
 	}
 
-	/* 4. NAT allow */
-	if (bsc->nat->imsi_allow) {
-		if (regexec(&bsc->nat->imsi_allow_re, mi_string, 0, NULL, 0) == 0)
-			return 0;
-	} else {
-		return 0;
-	}
-
-	/* unmatched */
-	return -3;
+	return 0;
 }
 
 static int _cr_check_loc_upd(struct bsc_connection *bsc, uint8_t *data, unsigned int length)
diff --git a/openbsc/src/nat/bsc_nat_vty.c b/openbsc/src/nat/bsc_nat_vty.c
index c41929e..3e572ba 100644
--- a/openbsc/src/nat/bsc_nat_vty.c
+++ b/openbsc/src/nat/bsc_nat_vty.c
@@ -52,8 +52,6 @@
 static int config_write_nat(struct vty *vty)
 {
 	vty_out(vty, "nat%s", VTY_NEWLINE);
-	if (_nat->imsi_allow)
-		vty_out(vty, " imsi allow %s%s", _nat->imsi_allow, VTY_NEWLINE);
 	if (_nat->imsi_deny)
 		vty_out(vty, " imsi deny %s%s", _nat->imsi_deny, VTY_NEWLINE);
 	vty_out(vty, " msc ip %s%s", _nat->msc_ip, VTY_NEWLINE);
@@ -233,16 +231,6 @@
 	return CMD_SUCCESS;
 }
 
-DEFUN(cfg_nat_imsi_allow,
-      cfg_nat_imsi_allow_cmd,
-      "imsi allow [REGEXP]",
-      "Allow matching IMSIs to talk to the MSC. "
-      "The defualt is to allow everyone.")
-{
-	bsc_parse_reg(_nat, &_nat->imsi_allow_re, &_nat->imsi_allow, argc, argv);
-	return CMD_SUCCESS;
-}
-
 DEFUN(cfg_nat_imsi_deny,
       cfg_nat_imsi_deny_cmd,
       "imsi deny [REGEXP]",
@@ -462,7 +450,6 @@
 	install_element(CONFIG_NODE, &cfg_nat_cmd);
 	install_node(&nat_node, config_write_nat);
 	install_default(NAT_NODE);
-	install_element(NAT_NODE, &cfg_nat_imsi_allow_cmd);
 	install_element(NAT_NODE, &cfg_nat_imsi_deny_cmd);
 	install_element(NAT_NODE, &cfg_nat_msc_ip_cmd);
 	install_element(NAT_NODE, &cfg_nat_msc_port_cmd);