Don't generate /etc/environment

/etc/environment, if it exists, should be a list of NAME=VALUE pairs,
not a shell script.  See the pam_env manpage.

modules/config/shells-environment.nix

@@ -144,7 +144,7 @@ in
         /bin/sh
       '';
 
-    environment.etc."environment".text =
+    system.build.setEnvironment = pkgs.writeText "set-environment"
        ''
          ${concatStringsSep "\n" (
            (mapAttrsToList (n: v: ''export ${n}="${concatStringsSep ":" v}"'')

modules/programs/bash/bash.nix

@@ -119,7 +119,7 @@ in
     programs.bash = {
 
       shellInit = ''
-        . /etc/environment
+        . ${config.system.build.setEnvironment}
 
         ${cfge.shellInit}
       '';

modules/programs/zsh/zsh.nix

@@ -87,7 +87,7 @@ in
     programs.zsh = {
 
       shellInit = ''
-        . /etc/environment
+        . ${config.system.build.setEnvironment}
 
         ${cfge.shellInit}
       '';