Deprecate admin_created_user_subject()

When `admin_created_user_subjec()` was merged from MU, the accompanying filter was left behind. As it has never been used by WordPress core, and is not an otherwise useful function, it can be deprecated.

Fixes #29915


git-svn-id: https://develop.svn.wordpress.org/trunk@30005 602fd350-edb4-49c9-b593-d223f7449a82
Begin cleanup of ms-sites group unit tests

* Split `test_create_and_delete_blog()` into two tests.
* Clean up number of sites created during tests.
* Remove test_getters(), move get_blog_address_by_name() test to `test_created_site_details()`

See #30080


git-svn-id: https://develop.svn.wordpress.org/trunk@30006 602fd350-edb4-49c9-b593-d223f7449a82
Improve tests for get_blog_id_from_url()

Expand tests to cover additional cache and lookup scenarios. Explicitly test the reaction of `get_blog_id_from_url()` when `$drop = false` is passed to `wpmu_delete_blog()`. See #30080

Fixes #30088


git-svn-id: https://develop.svn.wordpress.org/trunk@30007 602fd350-edb4-49c9-b593-d223f7449a82