remove code copied from gist

[pjfanning]

• the code has no license specified
• if it turns out that we need this test code, we will need to either see if scalatest supports retries now (eventually works well)
• or approach the author to see if he will grant us permission to license the gist

[mdedetrich]

I think this can be replaced with what I did in apache/pekko#471 or with something like

lazy val root = Project("test", file(".")).
  settings(commands += Command.command("testUntilFailed") { state =>
    "test" :: "testUntilFailed" :: state
  })

Which lets you run tests until they fail. I am actually thinking of putting both of these into an sbt-plugin (under my org) because they are generally useful.

[mdedetrich]

lgtm