Don't update a blog's last_updated time for all post deletions. Update only...

Don't update a blog's last_updated time for all post deletions. Update only when published posts are deleted.

Props SergeyBiryukov
fixes #20433


git-svn-id: https://core.svn.wordpress.org/trunk@20461 1a063a9b-81f0-0310-95a4-ce76da25c4cd