Remove generated codegen tests, move all testData to box/

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

compiler/testData/codegen/box/innerNested/nestedClassObject.kt

@@ -0,0 +1,12 @@
+class Outer {
+    class Nested {
+        class object {
+            val O = "O"
+            val K = "K"
+        }
+    }
+    
+    fun O() = Nested.O
+}
+
+fun box() = Outer().O() + Outer.Nested.K