Revert "Properly handle fwupd update capsules"

[blitz]

Reverts #113. Users have reported issues:

error: The option `environment.etc."fwupd/uefi_capsule.conf".source' has conflicting definition values:
       - In `/nix/store/s2lni0idfkhs0lcnr8walzhdqzarfb0m-source/nixos/modules/system/etc/etc.nix': <derivation etc-uefi_capsule.conf>
       - In `/nix/store/s2lni0idfkhs0lcnr8walzhdqzarfb0m-source/nixos/modules/services/hardware/fwupd.nix': "/nix/store/nxv27wliyqqdxvp44mx715d2v568k9ym-fwupd-1.8.10/etc/fwupd/uefi_capsule.conf"
       Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.