[tab_grid] Remove unnecessary code

Remove unnecessary collection view -reloadData call in -viewWillAppear.

BUG=686770

Review-Url: https://codereview.chromium.org/2714363002
Cr-Commit-Position: refs/heads/master@{#453254}

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

@@ -85,7 +85,6 @@ const CGFloat kToolbarHeight = 64.0f;
 }
 
 - (void)viewWillAppear:(BOOL)animated {
-  [self.grid reloadData];
   self.floatingNewTabButton = [MDCFloatingButton cr_tabGridNewTabButton];
   [self.floatingNewTabButton
       setFrame:[MDCFloatingButton