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/defArgs2.kt

@@ -0,0 +1,13 @@
+class A(val a: Int = 0, val b: String = "a")
+
+fun box(): String {
+  val a1 = A()
+  val a2 = A(1)
+  val a3 = A(b = "b")
+  val a4 = A(2, "c")
+  if (a1.a != 0 && a1.b != "a") return "fail"
+  if (a2.a != 1 && a2.b != "a") return "fail"
+  if (a3.a != 0 && a3.b != "b") return "fail"
+  if (a4.a != 2 && a4.b != "c") return "fail"
+  return "OK"
+}