Revert temporary fix for "store path ... is not allowed to have references"

The issue is now solved upstream: https://github.com/NixOS/nix/issues/5410

deploy.sh

@@ -6,7 +6,7 @@ cd "$(dirname "$0")"
 if ! command -v nix-build &> /dev/null
 then
 	echo "Nix installation could not be found. Please follow the instructions linked below."
-	echo "https://nixos.org/manual/nix/unstable/installation/installing-binary.html#multi-user-installation"
+	echo "https://nixos.org/manual/nix/unstable/installation/installing-binary.html"
 	exit
 fi
 
@@ -24,13 +24,12 @@ fi
 echo "deploying $host to $target"
 sleep 1
 
-tmp=$(mktemp -d)
-trap 'rm -rf "$tmp"' EXIT
-sources="$tmp/sources"
-cp -r $(nix-build nix/sources-dir.nix --no-out-link) $tmp/sources
-
 set -x
-system_drv=$(nix-instantiate "<nixpkgs/nixos>" -A config.system.build.toplevel -I $sources -I "nixos-config=$PWD/hosts/$host/configuration.nix")
+system_drv=$(
+  nix-instantiate "<nixpkgs/nixos>" -A config.system.build.toplevel \
+    -I "$(nix-build nix/sources-dir.nix --no-out-link)" \
+    -I "nixos-config=$PWD/hosts/$host/configuration.nix"
+)
 nix-copy-closure --to $target $system_drv
 system=$(ssh $target "nix-store --realise $system_drv")
 ssh $target "sudo nix-env -p /nix/var/nix/profiles/system -i $system && sudo /nix/var/nix/profiles/system/bin/switch-to-configuration $mode"