Customize: Ensure `changeset_uuid` param for autosave auto-draft gets stripped...

Customize: Ensure `changeset_uuid` param for autosave auto-draft gets stripped from location after previewing theme switch when not in branching mode.

Amends [41597].
See #39896.
Fixes #42415.

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git-svn-id: https://core.svn.wordpress.org/trunk@41943 1a063a9b-81f0-0310-95a4-ce76da25c4cd