Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/functions/kt1739.kt

@@ -0,0 +1,11 @@
+public class RunnableFunctionWrapper(val f : () -> Unit) : Runnable {
+    public override fun run() {
+        f()
+    }
+}
+
+fun box() : String {
+  var res = ""
+  RunnableFunctionWrapper({ res = "OK" }).run()
+  return res
+}