[ios] Fix the TabStrip for Fullscreen.

This CL fixed the tabStrip position in the fullscreen.

Bug: 1128249,1139770
Change-Id: I56fa6f03c758f9103e55e74a0069b79103c39d4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2519976
Commit-Queue: Nazerke Kalidolda <nazerke@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825249}

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -991,7 +991,7 @@ NSString* const kBrowserViewControllerSnackbarCategory =
                                 headerBehaviour:Hideable]];
     }
   } else {
-    if (self.tabStripView && !base::FeatureList::IsEnabled(kModernTabStrip)) {
+    if (self.tabStripView) {
       [results addObject:[HeaderDefinition definitionWithView:self.tabStripView
                                               headerBehaviour:Hideable]];
     }