Multisite: Revert [41719].

While `get_site_by()` makes sense as a more explicit and less complex replacement for `get_blog_details()`, it is not ready yet in terms of caching, where it currently falls short of the older function under specific circumstances.

See #40180, #40228.

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git-svn-id: https://core.svn.wordpress.org/trunk@41717 1a063a9b-81f0-0310-95a4-ce76da25c4cd