Delete the unused aws/lambda/github-webhook-rds-sync

[CliveUnger]

I am curious what the purpose of the github-webhook-rds-sync is. My understanding from https://github.com/pytorch/test-infra/blob/main/torchci/docs/architecture.md is that all data is pushed to a DynamoDB database via the PyTorchBot, so I want to understand how the RDS MySQL database is incorporated into the architecture. Thanks.

[ZainRizvi]

This is dead code and should be deleted

[CliveUnger]

I created a PR to delete the dead code. Not sure if anything else should be deleted as well.