Skip execution of aliases_program in newaliases script if value is "none"

Created by: racke

This fixes an annoying error message. The problem is more or less cosmetic as the aliases are already probably updated.

~$ sympa --close_list test
err main::#144 Invalid aliases_program "none"
close_list [notice] List has been closed

Sympa version: 6.2.59b.2

Relevant configuration:

sendmail_aliases /etc/mail/sympa/aliases
alias_manager Template
aliases_program none
aliases_wrapper off