db: Fix fall-out with the subscriber removal in the subscriber deletion code

The sender_id is gone so the code that attempted to delete SMS
didn't work anymore. Delete the SMS based on src_addr or the
dest_addr.

Fixes:
======================================================================
ERROR: testSubscriberAddRemove (__main__.TestCtrlNITB)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests/ctrl_test_runner.py", line 379, in testSubscriberAddRemove
    r = self.do_set('subscriber-delete-v1', '2620345')
  File "tests/ctrl_test_runner.py", line 114, in do_set
    return self.recv_msgs()[id]
KeyError: 1002
diff --git a/openbsc/src/libmsc/db.c b/openbsc/src/libmsc/db.c
index 1580acd..90c66c8 100644
--- a/openbsc/src/libmsc/db.c
+++ b/openbsc/src/libmsc/db.c
@@ -1042,8 +1042,8 @@
 	dbi_result_free(result);
 
 	result = dbi_conn_queryf(conn,
-			"DELETE FROM SMS WHERE sender_id=%llu OR receiver_id=%llu",
-			subscr->id, subscr->id);
+			"DELETE FROM SMS WHERE src_addr=%s OR dest_addr=%s",
+			subscr->extension, subscr->extension);
 	if (!result) {
 		LOGP(DDB, LOGL_ERROR,
 			"Failed to delete SMS for %llu\n", subscr->id);