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