Remove iOS 7 UICollectionView delegate API support

Summary: Don't need support for iOS 7 anymore, save some cycles on layout.

Reviewed By: ocrickard

Differential Revision: D4098229

fbshipit-source-id: eeaaf875acda1229f9622f11acc7c77ccad75cf0

Source/IGListCollectionView.m

@@ -9,21 +9,11 @@
 
 #import "IGListCollectionView.h"
 
-@interface IGListCollectionView ()
-
-@property (nonatomic, assign, readonly) BOOL requiresManualWillDisplay;
-@property (nonatomic, strong) NSSet *ig_visibleIndexPaths;
-
-@end
-
 @implementation IGListCollectionView
 
 - (void)commonInit {
     self.backgroundColor = [UIColor whiteColor];
     self.alwaysBounceVertical = YES;
-
-    // iOS 6 and 7 do not support -collectionView:willDisplayCell:forItemAtIndexPath: so we do it ourselves
-    _requiresManualWillDisplay = [[[UIDevice currentDevice] systemVersion] floatValue] < 8.0;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout {
@@ -49,17 +39,6 @@ - (void)layoutSubviews {
     [UIView performWithoutAnimation:^{
         [super layoutSubviews];
     }];
-
-    if (self.requiresManualWillDisplay && [self.delegate respondsToSelector:@selector(collectionView:willDisplayCell:forItemAtIndexPath:)]) {
-        NSArray *indexPaths = [self indexPathsForVisibleItems];
-        for (NSIndexPath *path in indexPaths) {
-            if (![self.ig_visibleIndexPaths containsObject:path]) {
-                UICollectionViewCell *cell = [self cellForItemAtIndexPath:path];
-                [self.delegate collectionView:self willDisplayCell:cell forItemAtIndexPath:path];
-            }
-        }
-        self.ig_visibleIndexPaths = [NSSet setWithArray:indexPaths];
-    }
 }
 
 @end