Images from a gallery are not displayed in the RSS feed.

<img width="520" height="496" alt="Image" src="https://github.com/user-attachments/assets/848da398-ed3e-48a3-b1c8-80d55556545c" />

Since FP 1.4, the PhotoSwipe overlay corset is located in the footer, so the problem of the overlay buttons being displayed in the RSS feed no longer exists. We can therefore remove `is_rss_feed()`.