get_patch_from_maildir: Workaround for RHEL 6 chainreply.

 * RHEL 6 chainreply will put all patches in reply to given email
   if git send-email 'reply to' provided.

 * Remove argparser.

 * Remove support of searching base on message id.

 * Simply use this command to get patches:
    get_patch_from_maildir $maildir_path $email_subject

Signed-off-by: Gris Ge <cnfourt@gmail.com>