Use upstream sbt-multi-jvm

[mdedetrich]

Now that sbt-multi-jvm is better maintained, we should have a look into using the upstream sbt-multi-jmv rather than our own inner sourced one

@He-Pin @jrudolph @raboof I remember having a discussion some time ago on the reasons why Pekko is using our own version of sbt-multi-jvm, I think that there are some adjustments that had to be made and if so we should upstream them?

[He-Pin]

Great, But we should detailly diff what the difference is.

[mdedetrich]

Great, But we should detailly diff what the difference is.

That's the point of the issue

[He-Pin]

@mdedetrich @pjfanning I think we should do this. the more code we can reduce the lightbend code the better