Remove old & unused BatteryManager::canSuspend() implementation.

Source/modules/battery/BatteryManager.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BatteryManager_h
 #define BatteryManager_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/ContextLifecycleObserver.h"
@@ skipping 30 matching lines @@
     DEFINE_ATTRIBUTE_EVENT_LISTENER(dischargingtimechange);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(levelchange);
 
     // Inherited from PlatformEventController.
     virtual void didUpdateData() override;
     virtual void registerWithDispatcher() override;
     virtual void unregisterWithDispatcher() override;
     virtual bool hasLastData() override;
 
     // ActiveDOMObject implementation.
-    virtual bool canSuspend() const { return true; }
     virtual void suspend() override;
     virtual void resume() override;
     virtual void stop() override;
     virtual bool hasPendingActivity() const override;
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     enum State {
         NotStarted,
         Pending,
         Resolved,
     };
 
     explicit BatteryManager(ExecutionContext*);
 
     RefPtrWillBeMember<ScriptPromiseResolver> m_resolver;
     Member<BatteryStatus> m_batteryStatus;
     State m_state;
 };
 
 } // namespace blink
 
 #endif // BatteryManager_h