Misleading logs suggesting that the security mails about clear passwords were not sent

XWIKI-19869 came with a migration which, among other things, warn user who had their password stored in clear.

The problem is that the migration log an error when the mail was not sent after a few seconds, but we wait between each mail by default to not be seen as spammer, so the result is that the admin gets scary logs for most impacted users while the mails are actually eventually sent.

IMO, we should just remove this timeout check.