Get rid of kotlin.Unit usage in RMI interfaces

attempt to fight mysterous "Cannot instantiate kotlin.Unit" exception.

jps-plugin/src/org/jetbrains/kotlin/compilerRunner/JpsCompilerServicesFacadeImpl.kt

@@ -32,9 +32,10 @@ internal class JpsCompilerServicesFacadeImpl(
                                          port),
         JpsCompilerServicesFacade {
 
-    override fun report(category: Int, severity: Int, message: String?, attachment: Serializable?) {
+    override fun report(category: Int, severity: Int, message: String?, attachment: Serializable?): Void? {
         env.messageCollector.reportFromDaemon(
                 { outFile, srcFiles -> env.outputItemsCollector.add(srcFiles, outFile) },
                 category, severity, message, attachment)
+        return null
     }
 }