[ios] Close all only visible panel

Previously, the close all button in regular tabs panel in tab grid would
close both the regular tabs and incognito tabs. This was the behavior
in the stack view.

This CL makes it only close the visible panel, as that makes more sense.

Bug: 845496
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I730f7c102baaf96e983543baa42d277414339b90
Reviewed-on: https://chromium-review.googlesource.com/1120680Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571911}

ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

@@ -920,7 +920,6 @@ NSUInteger GetPageIndexFromPage(TabGridPage page) {
       if (self.undoCloseAllAvailable) {
         [self.regularTabsDelegate undoCloseAllItems];
       } else {
-        [self.incognitoTabsDelegate closeAllItems];
         [self.regularTabsDelegate saveAndCloseAllItems];
       }
       self.undoCloseAllAvailable = !self.undoCloseAllAvailable;