Veja as opções para -R (remover) em man pacman , principalmente -u :
-u, --unneeded
Removes targets that are not required by any other packages. This is mostly useful when removing a group without using the -c option, to avoid breaking any dependencies.
Para pular as verificações de dependência, adicione a opção -d :
-d, --nodeps
Skips dependency version checks. Package names are still checked. Normally, pacman will always check a package’s dependency fields to ensure that all dependencies are installed and there are no package conflicts in the system. Specify this option twice to skip all dependency checks.
Assim, seu comando final seria pacman -Rdsu gnome-extra .