Remove the compiler plugin from this repo in favor /JetBrains/kotlin

[Jolanrensen]

Now the compiler plugin is a part of the Kotlin repo: https://github.com/JetBrains/kotlin/tree/master/plugins/kotlin-dataframe it can safely be removed from the project here.

We might need some migration here, to inform our users where to report issues with the library (here) and with the compiler plugin (YouTrack?).
Also, it might be worth investigating whether we can automate compatibility checks between our master branch and the compiler plugin