Revert "[ASLayoutSpec] Use childrenMap directly to prevent creating an NSArray within ASDK Part 2 (#2021)"

This reverts commit d5a7c19522.

AsyncDisplayKitTests/ASDisplayNodeTests.m

@@ -1723,24 +1723,6 @@ static inline BOOL _CGPointEqualToPointWithEpsilon(CGPoint point1, CGPoint point
   XCTAssertEqual(1, view.subviews.count, @"View should have 1 subview");
 }
 
-- (void)testFastEnumeration
-{
-  ASDisplayNode *parent = [[ASDisplayNode alloc] init];
-  
-  NSMutableArray *children = [NSMutableArray array];
-  for (int i = 0; i < 100; i++) {
-    ASDisplayNode *child = [[[ASDisplayNode alloc] init] autorelease];
-    [children addObject:child];
-    [parent addSubnode:child];
-  }
-  
-  NSInteger i = 0;
-  for (ASDisplayNode *child in parent) {
-    XCTAssertEqualObjects(child, children[i]);
-    i++;
-  }
-}
-
 - (void)checkBackgroundColorOpaqueRelationshipWithViewLoaded:(BOOL)loaded layerBacked:(BOOL)isLayerBacked
 {
   ASDisplayNode *node = [[ASDisplayNode alloc] init];