Remove unnecessary dag variables

Also remove a few trailing whitespaces.

modules/programs/msmtp.nix

@@ -6,8 +6,6 @@ let
 
   cfg = config.programs.msmtp;
 
-  dag = config.lib.dag;
-
   msmtpAccounts = filter (a: a.msmtp.enable)
     (attrValues config.accounts.email.accounts);
 

modules/programs/notmuch.nix

@@ -4,8 +4,6 @@ with lib;
 
 let
 
-  dag = config.lib.dag;
-
   cfg = config.programs.notmuch;
 
   mkIniKeyValue = key: value:

modules/services/polybar.nix

@@ -6,8 +6,6 @@ let
 
   cfg = config.services.polybar;
 
-  dag = config.lib.dag;
-
   toPolybarIni = generators.toINI {
     mkKeyValue = key: value:
       let

modules/services/window-managers/i3.nix

@@ -6,8 +6,6 @@ let
 
   cfg = config.xsession.windowManager.i3;
 
-  dag = config.lib.dag;
-
   commonOptions = {
     fonts = mkOption {
       type = types.listOf types.string;

modules/services/window-managers/xmonad.nix

@@ -6,8 +6,6 @@ let
 
   cfg = config.xsession.windowManager.xmonad;
 
-  dag = config.lib.dag;
-
   xmonad = pkgs.xmonad-with-packages.override {
     ghcWithPackages = cfg.haskellPackages.ghcWithPackages;
     packages = self: