There's a closed pull request on the void-packages repository

shotwell: remove unused dependency on libunique
https://github.com/void-linux/void-packages/pull/38871

Description:
https://gitlab.gnome.org/GNOME/shotwell/-/commit/7c2e51d3bbf9457d4dd37c60e3f59055c3923cbf

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#### Testing the changes
- I tested the changes in this PR: **briefly**

shotwell hasn't depended on libunique since 2012.

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