Deletes a list of files.  On success, it returns the number of files
it successfully deleted.  On failure, it returns false and sets $!
(errno):
On error, unlink will not tell you which files it could not remove.
If you want to know which files you could not remove, try them one
at a time:
Note: unlink will not attempt to delete directories unless you are
superuser and the -U flag is supplied to Perl.  Even if these
conditions are met, be warned that unlinking a directory can inflict
damage on your filesystem.  Finally, using unlink on directories is
not supported on many operating systems.  Use rmdir instead.
If LIST is omitted, unlink uses $_
.