Delete generated test cases, move testData to boxWithStdlib

compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/overriddenProperty.kt

@@ -0,0 +1,11 @@
+open data class A(open val x: String)
+
+class B : A("Fail") {
+    override val x: String = "OK"
+}
+
+fun foo(a: A) = a
+
+fun box(): String {
+    return if ("${foo(B())}" == "A(x=OK)") "OK" else "fail"
+}