Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/enum/valueof.kt

@@ -0,0 +1,11 @@
+enum class Color {
+  RED
+  BLUE
+}
+
+fun box() = if(
+     Color.valueOf("RED") == Color.RED
+  && Color.valueOf("BLUE") == Color.BLUE
+  && Color.values()[0] == Color.RED
+  && Color.values()[1] == Color.BLUE
+  ) "OK" else "fail"