Remove _ASDisplayLayer's delegateDidChangeBounds flag

We rely on the delegate setter to be called to set the flag. However, recent change on iOS 13 causes the setter to not be called at all and thus we had to put up a workaround (TextureGroup#1609). While the workaround works, the perf benefit of that the flag provides doesn't warranty the extra complexity IMO. So I think we should just remove everything.

Source/ASDisplayNode.mm

@@ -549,14 +549,6 @@ - (void)_locked_loadViewOrLayer
     _view = [self _locked_viewToLoad];
     _view.asyncdisplaykit_node = self;
     _layer = _view.layer;
-    // Needed to force `-[_ASDisplayLayer setDelegate:]` to evaluate
-    // It appears that UIKit might be setting the delegate ivar directly which
-    // bypasses establishing the `_delegateFlags` ivar on `ASDisplayLayer`
-    // This is critical for things like ASPagerNode, ASCollectionNode that depend
-    // on layer delegateFlags to forward bounds changes
-    if (_layer.delegate == _view) {
-      [_layer setDelegate:_view];
-    }
   }
   _layer.asyncdisplaykit_node = self;
 

Source/Details/_ASDisplayLayer.mm

@@ -22,22 +22,12 @@
 @implementation _ASDisplayLayer
 {
   BOOL _attemptedDisplayWhileZeroSized;
-
-  struct {
-    BOOL delegateDidChangeBounds:1;
-  } _delegateFlags;
 }
 
 @dynamic displaysAsynchronously;
 
 #pragma mark - Properties
 
-- (void)setDelegate:(id)delegate
-{
-  [super setDelegate:delegate];
-  _delegateFlags.delegateDidChangeBounds = [delegate respondsToSelector:@selector(layer:didChangeBoundsWithOldValue:newValue:)];
-}
-
 - (void)setDisplaySuspended:(BOOL)displaySuspended
 {
   ASDisplayNodeAssertMainThread();
@@ -59,12 +49,11 @@ - (void)setBounds:(CGRect)bounds
   if (!valid) {
     return;
   }
-  if (_delegateFlags.delegateDidChangeBounds) {
+  if ([self.delegate respondsToSelector:@selector(layer:didChangeBoundsWithOldValue:newValue:)]) {
     CGRect oldBounds = self.bounds;
     [super setBounds:bounds];
     self.asyncdisplaykit_node.threadSafeBounds = bounds;
     [(id<ASCALayerExtendedDelegate>)self.delegate layer:self didChangeBoundsWithOldValue:oldBounds newValue:bounds];
-
   } else {
     [super setBounds:bounds];
     self.asyncdisplaykit_node.threadSafeBounds = bounds;