Java to Kotlin converter: replacing equals call to ==/!= and no redundant parethesis generation

#KT-4426 Fixed

j2k/tests/testData/ast/equals/Equals4.java

@@ -0,0 +1,6 @@
+//file
+class C{
+    boolean foo(String s1, String s2, String s3, String s4) {
+        return s1.equals(s2) == !s3.equals(s4)
+    }
+}