Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/objects/kt2675.kt

@@ -0,0 +1,16 @@
+class A() {
+
+    fun ok() = Foo.Bar.bar() + Foo.Bar.barv
+
+    private object Foo {
+        fun foo() = "O"
+        val foov = "K"
+
+        public object Bar {
+            fun bar() = foo()
+            val barv = foov
+        }
+    }
+}
+
+fun box() = A().ok()