disk_filesystem: Remove unused total_entries_in_directory member from Disk_Directory

src/core/file_sys/disk_filesystem.h

@@ -74,7 +74,6 @@ public:
     }
 
 protected:
-    u32 total_entries_in_directory;
     FileUtil::FSTEntry directory;
 
     // We need to remember the last entry we returned, so a subsequent call to Read will continue