Remove generated codegen tests, move all testData to box/

A single test file will be generated out of box/ directory

compiler/testData/codegen/box/defaultArguments/constructor/enum.kt

@@ -0,0 +1,11 @@
+enum class A(val a: Int = 1) {
+  FIRST: A()
+  SECOND: A(2)
+}
+
+fun box(): String {
+   if (A.FIRST.a == 1 && A.SECOND.a == 2) {
+      return "OK"
+   }
+   return "fail"
+}