Delete generated test cases, move testData to boxWithStdlib

compiler/testData/codegen/boxWithStdlib/dataClasses/mixedParams.kt

@@ -0,0 +1,8 @@
+data class A(var x: Int, y: Int, val z: Int)
+
+fun box(): String {
+    val a = A(1, 2, 3)
+    if (a.component1() != 1) return "Fail: ${a.component1()}"
+    if (a.component2() != 3) return "Fail: ${a.component2()}"
+    return "OK"
+}