Revert "Merge pull request #48122 from zimbatm/pkg-nixos-rebuild"

This reverts commit 10addad603, reversing
changes made to 7786575c6c.

NixOS scripts should be kept in the NixOS source tree, not in
pkgs. Moving them around is just confusing and creates unnecessary
code/history churn.

nixos/modules/installer/tools/nixos-build-vms/nixos-build-vms.sh

@@ -0,0 +1,57 @@
+#! @shell@ -e
+
+# Shows the usage of this command to the user
+
+showUsage() {
+    exec man nixos-build-vms
+    exit 1
+}
+
+# Parse valid argument options
+
+PARAMS=`getopt -n $0 -o h -l no-out-link,show-trace,help -- "$@"`
+
+if [ $? != 0 ]
+then
+    showUsage
+    exit 1
+fi
+
+eval set -- "$PARAMS"
+
+# Evaluate valid options
+
+while [ "$1" != "--" ]
+do
+    case "$1" in
+	--no-out-link)
+	    noOutLinkArg="--no-out-link"
+	    ;;
+	--show-trace)
+	    showTraceArg="--show-trace"
+	    ;;
+	-h|--help)
+	    showUsage
+	    exit 0
+	    ;;
+    esac
+    
+    shift
+done
+
+shift
+
+# Validate the given options
+
+if [ "$1" = "" ]
+then
+    echo "ERROR: A network expression must be specified!" >&2
+    exit 1
+else
+    networkExpr=$(readlink -f $1)
+fi
+
+# Build a network of VMs
+
+nix-build '<nixpkgs/nixos/modules/installer/tools/nixos-build-vms/build-vms.nix>' \
+    --argstr networkExpr $networkExpr $noOutLinkArg $showTraceArg