Remove the option ‘programs.bash.enable’

NixOS has a pervasive dependency on bash. For instance, the X11
session script sources /etc/profile to get a reasonable
environment. Thus we should not provide an option to disable bash.

Also, enabling zsh no longer sets ‘users.defaultUserShell’ to zsh, to
prevent a collision with bash's definition of the same
option. (Changing the default shell is also something that should be
left to the user.)

nixos/modules/programs/bash/bash.nix

@@ -40,6 +40,7 @@ in
 
     programs.bash = {
 
+      /*
       enable = mkOption {
         default = true;
         description = ''
@@ -52,6 +53,7 @@ in
         '';
         type = types.bool;
       };
+      */
 
       shellAliases = mkOption {
         default = config.environment.shellAliases // { which = "type -P"; };
@@ -114,7 +116,7 @@ in
 
   };
 
-  config = mkIf cfg.enable {
+  config = /* mkIf cfg.enable */ {
 
     programs.bash = {