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/ea33909.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    return justPrint(9 compareTo 4) 
+} 
+
+fun justPrint(value: Int): String {
+    return if (value > 0) "OK" else "Fail $value"
+}