Revert "Fixes Iterable#toString forcing elements"

This reverts commit 129e3a7
(pull request scala/scala#8554).

See discussion on scala/scala-dev#671

Author: SethTisue

library/src/scala/collection/Iterable.scala

@@ -68,12 +68,12 @@ trait Iterable[+A] extends IterableOnce[A]
   protected[this] def stringPrefix: String = "Iterable"
 
   /** Converts this $coll to a string.
+    *
+    *  @return   a string representation of this collection. By default this
+    *            string consists of the `className` of this $coll, followed
+    *            by all elements separated by commas and enclosed in parentheses.
     */
-  override def toString: String  =
-    this match {
-      case _: StrictOptimizedIterableOps[_, _, _] => mkString(className + "(", ", ", ")")
-      case _                                      => className + (if (isEmpty) "()" else "(<iterable>)")
-    }
+  override def toString = mkString(className + "(", ", ", ")")
 
   /** Analogous to `zip` except that the elements in each collection are not consumed until a strict operation is
     * invoked on the returned `LazyZip2` decorator.

library/src/scala/collection/concurrent/TrieMap.scala

@@ -1002,7 +1002,6 @@ final class TrieMap[K, V] private (r: AnyRef, rtupd: AtomicReferenceFieldUpdater
     else cachedSize()
   override def isEmpty: Boolean = size == 0
   override protected[this] def className = "TrieMap"
-  override def toString: String = mkString(className + "(", ", ", ")")
 
 }