This updates some more instances of comparing site IDs on Sites and Users screens in network admin to use `is_main_site()` for clarity. Follow-up to [12603], [13918], [22064], [38814], [41131], [55666]. See #58150. Built from https://develop.svn.wordpress.org/trunk@55672 git-svn-id: http://core.svn.wordpress.org/trunk@55184 1a063a9b-81f0-0310-95a4-ce76da25c4cd