Issue 5183 - make FileSystemPtr std::unique_ptr

include/AdblockPlus/IFileSystem.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
@@ skipping 107 matching lines @@
     /**
      * Retrieves information about a file.
      * @param fileName File name.
      * @param callback The function called on completion.
      */
     virtual void Stat(const std::string& fileName,
                       const StatCallback& callback) const = 0;
   };
 
   /**
-   * Shared smart pointer to a `IFileSystem` instance.
+   * Unique smart pointer to to a `IFileSystem` instance.
    */
-  typedef std::shared_ptr<IFileSystem> FileSystemPtr;
+  typedef std::unique_ptr<IFileSystem> FileSystemPtr;
 }
 
 #endif