unimplement: do not delete methods which override super methods (IDEA-58918)

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/unimplement/before2String.java

@@ -0,0 +1,8 @@
+// "Unimplement Interface" "true"
+class A implements I<caret>I {
+  public String toString() {
+    return super.toString();
+  }
+}
+
+interface II {}