Get rid of `go-bindata` as it's not maintained anymore

The original author of `go-bindata` deleted their github account and someone else remade the repo with the _exact same name_. This is a bit sketchy. I also couldn't find any `go-bindata` forks that appear to be actively maintained.

We could keep using this tool, but it seems like we should go back to just having a `fixtures` directory with some certs for testing, as required.