KT-5287 J2K: Convert class with private constructor and static functions to "object" instead of class with "class object"

#KT-5287 Fixed

j2k/testData/fileOrElement/function/main.kt

@@ -1,4 +1,2 @@
-companion object {
-    public fun main(args: Array<String>) {
-    }
+public fun main(args: Array<String>) {
 }

j2k/testData/fileOrElement/function/main2.kt

@@ -1,7 +1,5 @@
-public class A {
-    companion object {
-        public fun main(args: Array<String>) {
-        }
+public object A {
+    public fun main(args: Array<String>) {
     }
 }
 

j2k/testData/fileOrElement/function/mainAndNullabilitySetting.kt

@@ -1,8 +1,6 @@
 // !forceNotNullTypes: false
-public class A {
-    companion object {
-        public fun main(args: Array<String>) {
-        }
+public object A {
+    public fun main(args: Array<String>) {
     }
 }