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()