Remove the ngrok platform binaries from the repository

Having the `ngrok[.exe]` binaries as part of the repository significantly increase the size of the repository, is less than ideal, doesn't (currently) cover all platforms (no macOS binary), and can easily get outdated. Keeping the committed binaries up to date would only cause a quick increase to the size of the repository.

Instead, we should either have scripts (platform-specific or agnostic) which can get ensure that we're running the latest, or include some documentation about [ngrok](https://ngrok.com) being a recommended development-time utility, with basic instructions on getting it and running it.