Android: Stop using custom path for GameFileCache

Back when I wrote this code, I believe I set it to use a custom path
so that the cache would end up in a directory which Android considers
to be a cache directory. But nowadays the directory which Dolphin's
C++ code considers to be the cache directory is such a directory,
so there's no longer any reason to override the default path.

Source/Core/UICommon/GameFileCache.h

@@ -31,8 +31,7 @@ public:
     Yes = 1,
   };
 
-  GameFileCache();  // Uses the default path
-  explicit GameFileCache(std::string path);
+  GameFileCache();
 
   void ForEach(std::function<void(const std::shared_ptr<const GameFile>&)> f) const;