Short Answer
Based on the facts you supplied, it seems the author's request for removal might be unenforceable.
Explanation
Section 2.a.1. of the license declares the license is irrevocable.
[Emphasis added]:
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.
Irrevocable means:
"Unable to cancel or recall; that which is unalterable or irreversible."
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