Customize: Ensure `changeset_uuid` query param is removed from the...

Customize: Ensure `changeset_uuid` query param is removed from the `customize.php` window's location once a changeset has been published (committed) with starter content.

Props westonruter, dlh for testing.
See #30937.
Fixes #39081.

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git-svn-id: https://core.svn.wordpress.org/trunk@39444 1a063a9b-81f0-0310-95a4-ce76da25c4cd