clean up IGListExperimentKeepPointerToCollectionViewDataSource

Summary: QE launched and reduced crashes, so lets clean up

Differential Revision: D60184705

fbshipit-source-id: 574b0228e3efadf7bd3bd0677a4373a3b95888d1

Source/IGListDiffKit/IGListExperiments.h

@@ -20,8 +20,6 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
     IGListExperimentInvalidateLayoutForUpdates = 1 << 2,
     /// Throw NSInternalInconsistencyException during an update
     IGListExperimentThrowOnInconsistencyException = 1 << 3,
-    /// Test keeping a strong pointer to the collectionView.dataSource during a batch update to avoid a crash
-    IGListExperimentKeepPointerToCollectionViewDataSource = 1 << 4,
 };
 
 /**

Source/IGListKit/Internal/IGListBatchUpdateTransaction.m

@@ -136,11 +136,10 @@ - (void)_didDiff:(IGListIndexSetResult *)diffResult onBackground:(BOOL)onBackgro
     [self.delegate listAdapterUpdater:self.updater didDiffWithResults:diffResult onBackgroundThread:onBackground];
 
     @try {
-        // Experiment with keeping a pointer to the self.collectionView.dataSource, because we're seeing a crash where it could be missing.
-        const BOOL keepDataSource = IGListExperimentEnabled(self.config.experiments, IGListExperimentKeepPointerToCollectionViewDataSource);
-        id<UICollectionViewDataSource> const collectionViewDataSource = keepDataSource ? self.collectionView.dataSource : nil;
-
-        if (self.collectionView.dataSource == nil || (keepDataSource && collectionViewDataSource == nil)) {
+        // Keeping a pointer to self.collectionView.dataSource, because it can get deallocated before the UICollectionView and crash
+        id<UICollectionViewDataSource> const collectionViewDataSource = self.collectionView.dataSource;
+
+        if (collectionViewDataSource == nil) {
             // If the data source is nil, we should not call any collection view update.
             [self _bail];
         } else if (diffResult.changeCount > 100 && self.config.allowsReloadingOnTooManyUpdates) {