Revert "Android: Don't hold gameFileCache lock during updateAdditionalMetadata"

This reverts commit fb265b610d.

The optimization in that commit is safe when the executor thread is
writing and the GUI thread is reading, but I had failed to take into
account that it's unsafe when the GUI thread is writing and the executor
thread is reading. (The native UpdateAdditionalMetadata function loops
through m_cached_files, which is unsafe if another thread is adding
elements to m_cached_files simultaneously.)

Losing out on this optimization isn't too bad, because
719930bb39 makes it very unlikely that
both threads will want the lock at the same time.

Source/Core/UICommon/GameFileCache.cpp

@@ -4,7 +4,6 @@
 #include "UICommon/GameFileCache.h"
 
 #include <algorithm>
-#include <atomic>
 #include <cstddef>
 #include <functional>
 #include <list>
@@ -204,7 +203,7 @@ bool GameFileCache::UpdateAdditionalMetadata(std::shared_ptr<GameFile>* game_fil
   if (custom_cover_changed)
     copy->CustomCoverCommit();
 
-  std::atomic_store(game_file, std::move(copy));
+  *game_file = std::move(copy);
 
   return true;
 }