refactor db_subscr_purge

Use named parameters in the SQL statements.

Use db_bind_* functions to drop some code dup.

Adopt error handling (rc and logging) to match the other db functions: return
-ENOENT for unknown subscriber, -EIO for SQL failures.

Change-Id: Iad49d29b90a708c6cf55bfb3bcc02d9e29001a15
diff --git a/src/hlr.c b/src/hlr.c
index 9e8b699..b32f709 100644
--- a/src/hlr.c
+++ b/src/hlr.c
@@ -221,7 +221,7 @@
 	 * we have on record. Only update if yes */
 
 	/* Perform the actual update of the DB */
-	rc = db_subscr_purge(g_hlr->dbc, gsup->imsi, is_ps);
+	rc = db_subscr_purge(g_hlr->dbc, gsup->imsi, true, is_ps);
 
 	if (rc == 1)
 		gsup_reply.message_type = OSMO_GSUP_MSGT_PURGE_MS_RESULT;