Based on the facts you supplied, it seems the author's request for removal might be unenforceable.
Section 2.a.1. of the license declares the license is irrevocable.
Subject to the terms and conditions of this Public License, the Licensor hereby grants You a worldwide, royalty-free, non-sublicensable, non-exclusive, irrevocable license to exercise the Licensed Rights in the Licensed Material to:
A. reproduce and Share the Licensed Material, in whole or in part; and
B. produce, reproduce, and Share Adapted Material.
"Unable to cancel or recall; that which is unalterable or irreversible."
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