Remove unnecessary check of token validity from dice_browsertest.cc

dice_browsertest.cc checks the |is_valid| param in its implementation of
IdentityManager::Observer::OnRefreshTokenUpdatedForAccount(). This param
is slated for removal (see bug), so we need to change this. Happily,
(or unhappily), the tests do not depend on this check; it can just be
removed.

Bug: 908412
Change-Id: Id59c9370bf8258d077de689ee5ba55fd67d89f2e
Reviewed-on: https://chromium-review.googlesource.com/c/1353893Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612611}

chrome/browser/signin/dice_browsertest.cc

@@ -542,7 +542,7 @@ class DiceBrowserTestBase : public InProcessBrowserTest,
 
   void OnRefreshTokenUpdatedForAccount(const AccountInfo& account_info,
                                        bool is_valid) override {
-    if (is_valid && account_info.account_id == GetMainAccountID()) {
+    if (account_info.account_id == GetMainAccountID()) {
       refresh_token_available_ = true;
       RunClosureIfValid(std::move(refresh_token_available_quit_closure_));
     }