Template out V8 and prepare for other JS engine implementations

shell/src/GcCommand.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef GC_COMMAND_H
 #define GC_COMMAND_H
 
 #include <AdblockPlus.h>
 #include <string>
 
 #include "Command.h"
 
 class GcCommand : public Command
 {
 public:
-  explicit GcCommand(AdblockPlus::JsEngine& jsEngine);
+  GcCommand(AdblockPlus::JsEngine& jsEngine);
   void operator()(const std::string& arguments);
   std::string GetDescription() const;
   std::string GetUsage() const;
 
 private:
   AdblockPlus::JsEngine& jsEngine;
 };
 
 #endif