KT-2819 Duplicate toString() method generated in data class

#KT-2819 Fixed

compiler/testData/codegen/dataClasses/hashcode/alreadyDeclared.kt

@@ -0,0 +1,7 @@
+data class A(val x: Int) {
+  fun hashCode(): Int = -3
+}
+
+fun box(): String {
+  return if (A(0).hashCode() == -3) "OK" else "fail"
+}