nixos/terminfo: always use buildPlatform's terminfo (#309108)

Many terminal packages don't cross compile, so the `terminfo`
NixOS module was not usable for nixos configurations that are
cross-compiled.

Terminfo files (AFAIK) are small files that contain data about
terminal capability, so they should never have any runtime
dependencies that would cause any executables or otherwise
incompatible outputs from the `buildPlatform` to leak into the
nixos config's closure.

Changed files
+1 -1
nixos
modules
config
+1 -1
nixos/modules/config/terminfo.nix
···
# attrNames (filterAttrs
# (_: drv: (builtins.tryEval (isDerivation drv && drv ? terminfo)).value)
# pkgs)
-
environment.systemPackages = mkIf config.environment.enableAllTerminfo (map (x: x.terminfo) (with pkgs; [
+
environment.systemPackages = mkIf config.environment.enableAllTerminfo (map (x: x.terminfo) (with pkgs.pkgsBuildBuild; [
alacritty
contour
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