Cleanup mailPasswords when oidc client is removed not only when an app is uninstalled

src/mailpasswords.js

@@ -54,10 +54,17 @@ async function del(clientId, userId) {
     if (result.affectedRows !== 1) throw new BoxError(BoxError.NOT_FOUND, 'mail password not found');
 }
 
+async function purgeByClientId(clientId) {
+    assert.strictEqual(typeof clientId, 'string');
+
+    await database.query('DELETE FROM mailPasswords WHERE clientId = ?', [ clientId ]);
+}
+
 export default {
     get,
     getByUserId,
     add,
     list,
-    del
+    del,
+    purgeByClientId,
 };