[iOS] Don't reset the alert coordinator when cancel

It seems that resetting the alert coordinator is actually dismissing the
ReadingList ViewController.
This is not needed as nothing is relying on the coordinator to be nil,
so removing the nil assignment is working.

Fixed: 1105852
Change-Id: I1cf8c38e6f6b8d1f8456e6b2ed439e38c44db275
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316204
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791453}

ios/chrome/browser/ui/reading_list/context_menu/reading_list_context_menu_coordinator.mm

@@ -147,8 +147,6 @@ enum UMAContextMenuAction {
   // Add "Cancel" option.
   [self addItemWithTitle:l10n_util::GetNSString(IDS_APP_CANCEL)
                   action:^{
-                    [weakDelegate
-                        cancelReadingListContextMenuWithParams:weakParams];
                     UMA_HISTOGRAM_ENUMERATION("ReadingList.ContextMenu", CANCEL,
                                               ENUM_MAX);
                   }

ios/chrome/browser/ui/reading_list/context_menu/reading_list_context_menu_delegate.h

@@ -24,9 +24,6 @@
 // Opens the offline page at |offlineURL| in a new tab.
 - (void)openOfflineURLInNewTabForContextMenuWithParams:
     (ReadingListContextMenuParams*)params;
-// Cancels the context menu created with |params|.
-- (void)cancelReadingListContextMenuWithParams:
-    (ReadingListContextMenuParams*)params;
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_READING_LIST_CONTEXT_MENU_READING_LIST_CONTEXT_MENU_DELEGATE_H_

ios/chrome/browser/ui/reading_list/reading_list_coordinator.mm

@@ -226,11 +226,6 @@
            incognito:NO];
 }
 
-- (void)cancelReadingListContextMenuWithParams:
-    (ReadingListContextMenuParams*)params {
-  self.contextMenuCoordinator = nil;
-}
-
 #pragma mark - ReadingListTableViewControllerDelegate
 
 - (void)dismissReadingListListViewController:(UIViewController*)viewController {