Remove Java-related configuration from build.gradle for Kotlin projects

[wilkinsona]

I don't think target and source compatibility make sense:

sourceCompatibility = 1.8
targetCompatibility = 1.8

I'm also not sure about the configuration of Eclipse's classpath, but I'd have to look at Kotlin's Eclipse plugin more closely to be sure.

eclipse {
    classpath {
         containers.remove('org.eclipse.jdt.launching.JRE_CONTAINER')
         containers 'org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8'
    }
}

If the above isn't needed, then it might also be possible to stop applying the Eclipse plugin too.

[snicoll]

@wilkinsona the last bits are removed as part of #275 - As for the rest, isn't that there for cross-compilation? We do support java+groovy for Groovy-based projects. Doesn't it make sense for Kotlin-based projects? ping @sdeleuze

[sdeleuze]

While mixed Java + Kotlin project are common on existing Java project, I tend to think most Kotlin newly created projects will just use Kotlin code, so indeed that could make sense to remove sourceCompatibility and targetCompatibility.

[mhalbritter]

With the switch to toolchains in #1227 these bits have been removed.