Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/properties/kt2655.kt

@@ -0,0 +1,20 @@
+trait TextField {
+    fun getText(): String
+    fun setText(text: String)
+}
+
+class SimpleTextField : TextField {
+    private var text = ""
+    override fun getText() = text
+    override fun setText(text: String) {
+        this.text = text
+    }
+}
+
+class TextFieldWrapper(textField: TextField) : TextField by textField
+
+fun box() : String {
+    val textField = TextFieldWrapper(SimpleTextField())
+    textField.setText("OK")
+    return textField.getText()
+}