Use upstream sbt-multi-jvm

Now that [sbt-multi-jvm](https://github.com/sbt/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](https://github.com/apache/incubator-pekko/blob/main/project/SbtMultiJvm.scala)

@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?