Remove unnecessary array to list conversion in SplitLogManager

  public static List<FileStatus> getFileList(final Configuration conf, final List<Path> logDirs,
      final PathFilter filter)
      throws IOException {
    List<FileStatus> fileStatus = new ArrayList<>();
    ....
    FileStatus[] a = new FileStatus[fileStatus.size()];
    //list to array
    return fileStatus.toArray(a);
  }

  public List<FileStatus> getWALsToSplit(ServerName serverName, boolean splitMeta)
      throws IOException {
    List<Path> logDirs = master.getMasterWalManager().getLogDirs(Collections.singleton(serverName));
    FileStatus[] fileStatuses =
        SplitLogManager.getFileList(this.conf, logDirs, splitMeta ? META_FILTER : NON_META_FILTER);
    LOG.info("{} WAL count={}, meta={}", serverName, fileStatuses.length, splitMeta);
    //array convert to list which is just contrary to the logic of  getFileList
    return Lists.newArrayList(fileStatuses);