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/defArgs1.kt

@@ -0,0 +1,8 @@
+class A(val a: Int = 0)
+
+fun box(): String {
+   if (A().a == 0 && A(1).a == 1) {
+      return "OK"
+   }
+   return "fail"
+}