Attempt to fix an issue introduced by #548

[AmineChikhaoui]

The EC2 deployments evaluations are failing after the optionSet -> submodule PR merge.

[nix-shell:~/work/nixops]$ nixops info -d minimal-lb 
error: attribute ‘cipher’ missing, at /home/aminechikhaoui/work/nixops/nix/ec2.nix:461:10
(use ‘--show-trace’ to show detailed location information)
warning: evaluation of the deployment specification failed; status info may be incorrect

Removing the types.uniq looks like a possible fix but I wasn't able to understand the issue or why removing that is fixing it.

@domenkozar @rbvermaa any ideas ?

[edolstra]

I don't understand where the error message comes from, but the uniq seems unnecessary in any case. So let's merge this.