Fix a typo of comments in AutoVacLauncherMain

Hi,

While reading autovacuum.c, I found the following comments in
AutoVacLauncherMain() right before the call to rebuild_database_list();

* Create the initial database list. The invariant we want this list to
* keep is that it's ordered by decreasing next_time. As soon as an entry

However, I couldn't fnd any variable named "next_time". I believe it actually refers
to adl_next_worker and the comments should use "next_worker" as is done in other nereby
comments. I've attahed a patch to address this.

Regards,
Yugo Nagata

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>