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/kt395.kt

@@ -0,0 +1,12 @@
+fun Any.with(operation :  Any.() -> Any) = operation().toString()
+
+val f = { (a : Int) :Unit -> }
+
+fun box () : String {
+    return if(20.with {
+        this
+    } == "20")
+        "OK"
+    else
+        "fail"
+}