add missing apps.delPortBinding

this got lost in async/db translation

src/apps.js

@@ -10,6 +10,7 @@ exports = module.exports = {
     update,
     setHealth,
     del,
+    delPortBinding,
 
     get,
     getByIpAddress,
@@ -817,6 +818,14 @@ async function del(id) {
     if (results[5].affectedRows !== 1) throw new BoxError(BoxError.NOT_FOUND, 'App not found');
 }
 
+async function delPortBinding(hostPort, type) {
+    assert.strictEqual(typeof hostPort, 'number');
+    assert.strictEqual(typeof type, 'string');
+
+    const result = await database.query('DELETE FROM appPortBindings WHERE hostPort=? AND type=?', [ hostPort, type ]);
+    if (result.affectedRows !== 1) throw new BoxError(BoxError.NOT_FOUND, 'App not found');
+}
+
 async function clear() {
     await database.query('DELETE FROM subdomains');
     await database.query('DELETE FROM appPortBindings');