While `HideHelp` hides both `help` command and `--help` flag, `HideHelpCommand`
only hides `help` command and leave `--help` flag as-is.
The behavior of `HideHelp` is untouched in this commit.
Fix#523
Replace #636
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
