tmux module: set TMUX_TMPDIR via environment instead of wrapper

nixos/modules/programs/tmux.nix

@@ -156,8 +156,13 @@ in {
 
   config = mkIf cfg.enable {
     environment = {
-      systemPackages = [ pkgs.tmux ];
       etc."tmux.conf".text = tmuxConf;
+
+      systemPackages = [ pkgs.tmux ];
+
+      variables = {
+        TMUX_TMPDIR = ''''${XDG_RUNTIME_DIR:-"/run/user/\$(id -u)"}'';
+      };
     };
   };
 }

pkgs/tools/misc/tmux/default.nix

@@ -34,9 +34,6 @@ stdenv.mkDerivation rec {
   postInstall = ''
     mkdir -p $out/share/bash-completion/completions
     cp -v ${bashCompletion}/completions/tmux $out/share/bash-completion/completions/tmux
-
-    wrapProgram $out/bin/tmux \
-      --set TMUX_TMPDIR \''${XDG_RUNTIME_DIR:-"/run/user/\$(id -u)"}
   '';
 
   meta = {