Upgrade Dune to 3.12.1 from 3.8.3+shim

The shim is removed since Dune is no longer in the global environment.

Because no shim needed, might as well upgrade Dune to the latest
version (3.12.1).

Part of diskuv/dkml-installer-ocaml#83

src/none/dune-anyver-pkgs.txt

@@ -3,33 +3,36 @@
 
 # See README.md for a description of this file format.
 
-# Dune is needed to compile dkml-findup.exe
-# dune-* must be compatible with Dune
+# As of DkML 2.1.0, dune is not installed globally. But that non-installation
+# is performed by the gitlab.com/dkml/distributions/dkml's cmake scripts
+# (and dkml-component-desktop) only using the [ci] and [full] flavors, rather
+# than also this [dune] flavor.
 ##      global-install
 #       bin/dune
 #       bin/dune-real
 #       man/man1/dune-build.1
 #       man/man1/...
 #       man/man1/dune.1
 #       man/man5/dune-config.5
-dune.3.8.3+shim
-dune-action-plugin.3.8.3
-dune-build-info.3.8.3
-dune-configurator.3.8.3
-dune-glob.3.8.3
-dune-private-libs.3.8.3
-dune-rpc.3.8.3
-dune-rpc-lwt.3.8.3
-dune-site.3.8.3
-dyn.3.8.3
-# fiber is special; does not go past 3.7.0
+dune.3.12.1
+#   [dune-*] must be compatible with [dune]
+dune-action-plugin.3.12.1
+dune-build-info.3.12.1
+dune-configurator.3.12.1
+dune-glob.3.12.1
+dune-private-libs.3.12.1
+dune-rpc.3.12.1
+dune-rpc-lwt.3.12.1
+dune-site.3.12.1
+dyn.3.12.1
+#   fiber is special; does not go past 3.7.0
 fiber.3.7.0
-ordering.3.8.3
-stdune.3.8.3
+ordering.3.12.1
+stdune.3.12.1
 # xdg is a Dune related package but is listed separately
 
 ##      global-compile
 #       note: xdg.3.9.0+ is used by utop.2.13.0, and is independent from the
 #             rest of the Dune packages
 #       lib/stublibs/dllxdg_stubs.dll
-xdg.3.9.0
+xdg.3.12.1