[#75804242] Consolidate documentation on how to run the tests

Make our documentation consistent so that we only document one way of running the tests.

Do this by replacing the Makefile with a stub bash script and update the Travis CI configuration accordingly.
That's a good idea (done in a65f47c), although it didn't fix the `go get` issue in Travis. I was also unable to reproduce the `go get` issue on my local machine.