treewide: remove now-redundant lib.mdDoc calls

These (and the `*MD` functions apart from `literalMD`) are now no-ops
in nixpkgs and serve no purpose other than to add additional noise and
potentially mislead people into thinking unmarked DocBook documentation
will still be accepted.

Note that if backporting changes including documentation to 23.05,
the `mdDoc` calls will need to be re-added.

To reproduce this commit, run:

    $ NIX_PATH=nixpkgs=flake:nixpkgs/e7e69199f0372364a6106a1e735f68604f4c5a25 \
      nix shell nixpkgs#coreutils \
      -c find . -name '*.nix' \
      -exec nix run -- github:emilazy/nix-doc-munge/98dadf1f77351c2ba5dcb709a2a171d655f15099 \
      --strip {} +
    $ ./format

modules/programs/java.nix

@@ -14,8 +14,8 @@ in {
 
   options = {
     programs.java = {
-      enable = mkEnableOption (lib.mdDoc "") // {
-        description = lib.mdDoc ''
+      enable = mkEnableOption "" // {
+        description = ''
           Install the Java development kit and set the
           {env}`JAVA_HOME` variable.
         '';
@@ -25,7 +25,7 @@ in {
         type = types.package;
         default = pkgs.jdk;
         defaultText = "pkgs.jdk";
-        description = lib.mdDoc ''
+        description = ''
           Java package to install. Typical values are
           `pkgs.jdk` or `pkgs.jre`.
         '';