gS644 [1] filed a deletion request for nemo-seahorse-git [2]:

Since the package "nemo-seahorse" was moved to [community] and no one seems to have the wish to update this git version, it probably can be deleted. Both (with and without nautilus dependencies) are avaiable in the official repos [A] and in AUR [B]

[A] https://www.archlinux.org/packages/community/x86_64/nemo-seahorse/ [B] https://aur.archlinux.org/packages/nemo-seahorse-nonautilus

[1] https://aur.archlinux.org/account/gS644/ [2] https://aur.archlinux.org/pkgbase/nemo-seahorse-git/