Tests: Replace most instances of `wpmu_delete_blog()` not specifically testing...

Tests: Replace most instances of `wpmu_delete_blog()` not specifically testing that function with `wp_delete_site()`.

Follow-up to [47011].

See #47195.
Built from https://develop.svn.wordpress.org/trunk@47012


git-svn-id: https://core.svn.wordpress.org/trunk@46812 1a063a9b-81f0-0310-95a4-ce76da25c4cd