function unlink(path, callback) {
        appshell.fs.unlink(path, function (err) {
            callback(_mapError(err));
        });
    }
Unlink (i.e., permanently delete) the file or directory at the given path,
calling back asynchronously with a possibly null FileSystemError string.
Directories will be unlinked even when non-empty.

@param {string} path
@param {function(string)=} callback