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/nestedInPackage.kt

@@ -0,0 +1,10 @@
+package Package
+
+class Outer {
+    class Nested {
+        val O = "O"
+        val K = "K"
+    }
+}
+
+fun box() = Package.Outer.Nested().O + Outer.Nested().K