nemo-seahorse and libcryptui dependency

[billyswong]

According to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1118295, caja-seahorse is removed from Debian repository because of its dependency on libcryptui. nemo-seahorse, being a similar fork, is vulnerable to the same issue too.

[FabioLolix]

In Arch Linux too nemo-seahorse and libcryptui have been demoted from the official repository to the AUR

also nemo-preview have been dropped because it use clutter