minor optimizations

Author: jessesquires

JSQMessagesViewController/Controllers/JSQMessagesViewController.m

@@ -475,8 +475,6 @@ - (UICollectionViewCell *)collectionView:(JSQMessagesCollectionView *)collection
     cell.messageBubbleTopLabel.attributedText = [collectionView.dataSource collectionView:collectionView attributedTextForMessageBubbleTopLabelAtIndexPath:indexPath];
     cell.cellBottomLabel.attributedText = [collectionView.dataSource collectionView:collectionView attributedTextForCellBottomLabelAtIndexPath:indexPath];
 
-    cell.backgroundColor = [UIColor whiteColor];
-    
     CGFloat bubbleTopLabelInset = (avatarImageDataSource != nil) ? 60.0f : 15.0f;
 
     if (isOutgoingMessage) {