FcDirCacheUnlink - Remove all caches related to dir
       #include <fontconfig.h>
       FcBool FcDirCacheUnlink(const FcChar8 *dir);
       (FcConfig *config);
       .fi
       Scans  the  cache  directories in config, removing any instances of the
       cache file for dir. Returns FcFalse when  some  internal  error  occurs
       (out  of memory, etc). Errors actually unlinking any files are ignored.
       Fontconfig version 2.8.0
                               18 November 2009            FcDirCacheUnlink(3)