move all output modules to subdirectory, trash standard.nix

standard.nix isn't, is the essence here. Not all devices
support flashimage as it is currently defined - some
have diskimage, some have neither

modules/all-modules.nix

@@ -29,7 +29,6 @@
    ./ramdisk.nix
    ./squashfs.nix
    ./ssh
-   ./standard.nix
    ./tftpboot.nix
    ./ubifs.nix
    ./users.nix

modules/outputs/kexecboot.nix

@@ -7,7 +7,7 @@
 let
   inherit (lib) mkOption mkForce types concatStringsSep;
 in {
-  imports = [ ./ramdisk.nix ];
+  imports = [ ../ramdisk.nix ];
   options.system.outputs = {
     kexecboot = mkOption {
       type = types.package;

modules/outputs/tftpboot.nix

@@ -8,7 +8,7 @@ let
   inherit (lib) mkOption types concatStringsSep;
   cfg = config.boot.tftp;
 in {
-  imports = [ ./ramdisk.nix ];
+  imports = [ ../ramdisk.nix ];
   options.boot.tftp.freeSpaceBytes = mkOption {
     type = types.int;
     default = 0;

modules/standard.nix

@@ -1,12 +0,0 @@
-{
-  # "standard" modules that aren't fundamentally required,
-  # but are probably useful in most common workflows and
-  # you should have to opt out of instead of into
-  imports = [
-    ./tftpboot.nix
-    ./kexecboot.nix
-    ./outputs/flashimage.nix
-    ./jffs2.nix
-    ./ubifs.nix
-  ];
-}