Deletes a file, does nothing if the file does not exist

@param filename {String} file to delete
@async
function(filename) {
      return new Promise((resolve, reject) => {
        fs.unlink(filename, function(err) {
          if (err && err.code != "ENOENT") {
            reject(err);
          } else {
            resolve(); 
          }
        });
      });
    }