Remove unused class DiceTestTokenServiceObserver

This is a left over of https://crrev.com/c/1355189 ([signin] Delete
DiceFixAuthErrors).

TBR=droger@chromium.org

BUG= 777774

Change-Id: I89b6359df1c8910973ca3bcdc9c9145b89d5d464
Reviewed-on: https://chromium-review.googlesource.com/c/1394666Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#619914}

chrome/browser/signin/dice_response_handler_unittest.cc

@@ -80,28 +80,6 @@ class DiceTestSigninClient : public TestSigninClient, public GaiaAuthConsumer {
   DISALLOW_COPY_AND_ASSIGN(DiceTestSigninClient);
 };
 
-// Checks if OnRefreshTokenAvailable() has been called for the specified
-// account.
-class DiceTestTokenServiceObserver : public OAuth2TokenService::Observer {
- public:
-  explicit DiceTestTokenServiceObserver(const std::string& account_id)
-      : account_id_(account_id) {}
-
-  bool token_received() { return token_received_; }
-
- private:
-  // OAuth2TokenServiceObserver:
-  void OnRefreshTokenAvailable(const std::string& account_id) override {
-    if (account_id == account_id_)
-      token_received_ = true;
-  }
-
-  bool token_received_ = false;
-  std::string account_id_;
-
-  DISALLOW_COPY_AND_ASSIGN(DiceTestTokenServiceObserver);
-};
-
 class DiceResponseHandlerTest : public testing::Test,
                                 public AccountReconcilor::Observer {
  public: