Use INNER instead of LEFT JOIN for reminder and auto-close SQL for CCK node types

In working on #336255: CCK datestamp fields totally broken and fields without timezone handling mostly broken I noticed that we're doing a LEFT JOIN for the reminder and autoclose SQL for CCK date* fields. Since we do a separate query for each node type, when we join on the appropriate {content_*} table for the start date, I'm pretty sure we can INNER instead of LEFT JOIN there, which would be better for DB performance. I'll test that after lunch and commit a change if all looks good.