Add a TODO comments to remind that race condition exists and cleanup code should move to syncd

[sumanbrcm]

Description This is related to issue (https://github.com/Azure/sonic-swss/issues/2193) and the fix (https://github.com/Azure/sonic-swss/pull/2199) . All the details are mentioned in PR and the fix. As a follow-up , it was needed to add a comment to remind that a race condition exists and the cleanup should be done in syncd . This PR is only to add a comment in code , no other details (steps to reproduce, expected output etc) are necessary.