Removing .github/scale-config.yml, now this repo is using the config in test-infra

[jeanschmidt]

As communicated internally, all repositories now rely on a single scale-config.yml that is on pytorch/test-infra. As such this file is no longer used and to avoid confusion it is better to remove it.

Here is a short summary of the announcement:

As previously announced, the scale-config.yml file in each repository for the pytorch/ organization is now not being used to control GHA runners. On its place, the file with same path on test-infra repository is controlling and enabling runners. If you feel the need for new runners, or change settings for current ones, feel free to submit a PR with required changes on the former file.