Upgrader: Deprecate a few mostly unused functions, wp_update_plugin(), wp_update_theme(), and, wp_update_core().
wp_update_core() was still used, as it was never updated to make use of the newer Skins. Fixes #21874

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Switch to using HTTPS connections for Plugin and Theme API requests when SSL is available. See #18577

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WP_HTTP: Correct the @since, and, @deprecated PHPDoc tags to reflect the class history. See #25007

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