Remove unused/redundant implementation details.

js/js.libraries/src/core/collections/AbstractCollection.kt

@@ -32,8 +32,6 @@ public abstract class AbstractMutableCollection<E> protected constructor() : Abs
         return false
     }
 
-    override fun isEmpty(): Boolean = size == 0
-
     override fun addAll(elements: Collection<E>): Boolean {
         var modified = false
         for (element in elements) {
@@ -53,8 +51,7 @@ public abstract class AbstractMutableCollection<E> protected constructor() : Abs
         }
     }
 
-    // TODO: move somehow to AbstractCollection
-
+    // TODO: move somehow to AbstractCollection: can't move now, because it cannot be protected on JVM, just public
     protected open fun toArray(): Array<Any?> = copyToArrayImpl(this)
 
     open fun toJSON(): Any = this.toArray()

libraries/stdlib/src/kotlin/collections/AbstractList.kt

@@ -65,18 +65,12 @@ public abstract class AbstractList<out E> protected constructor() : AbstractColl
     private open inner class IteratorImpl : Iterator<E> {
         /** the index of the item that will be returned on the next call to [next]`()` */
         protected var index = 0
-        /** the index of the item that was returned on the previous call to [next]`()`
-         * or [ListIterator.previous]`()` (for `ListIterator`),
-         * -1 if no such item exists
-         */
-        protected var last = -1
 
         override fun hasNext(): Boolean = index < size
 
         override fun next(): E {
             if (!hasNext()) throw NoSuchElementException()
-            last = index++
-            return get(last)
+            return get(index++)
         }
     }
 
@@ -96,9 +90,7 @@ public abstract class AbstractList<out E> protected constructor() : AbstractColl
 
         override fun previous(): E {
             if (!hasPrevious()) throw NoSuchElementException()
-
-            last = --index
-            return get(last)
+            return get(--index)
         }
 
         override fun previousIndex(): Int = index - 1