Delete generated test cases, move testData to boxWithStdlib

compiler/testData/codegen/boxWithStdlib/dataClasses/equals/alreadyDeclared.kt

@@ -0,0 +1,8 @@
+data class A(val x: Int) {
+  fun equals(other: Any?): Boolean = false
+}
+
+fun box(): String {
+  val a = A(0)
+  return if (a equals a) "fail" else "OK"
+}