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/ncmpcpp.nix

@@ -31,14 +31,13 @@ let
     options = {
       key = mkOption {
         type = types.str;
-        description = lib.mdDoc "Key to bind.";
+        description = "Key to bind.";
         example = "j";
       };
 
       command = mkOption {
         type = with types; either str (listOf str);
-        description =
-          lib.mdDoc "Command or sequence of commands to be executed.";
+        description = "Command or sequence of commands to be executed.";
         example = "scroll_down";
       };
     };
@@ -48,14 +47,14 @@ in {
   meta.maintainers = [ hm.maintainers.olmokramer ];
 
   options.programs.ncmpcpp = {
-    enable = mkEnableOption
-      (lib.mdDoc "ncmpcpp - an ncurses Music Player Daemon (MPD) client");
+    enable =
+      mkEnableOption "ncmpcpp - an ncurses Music Player Daemon (MPD) client";
 
     package = mkOption {
       type = types.package;
       default = pkgs.ncmpcpp;
       defaultText = literalExpression "pkgs.ncmpcpp";
-      description = lib.mdDoc ''
+      description = ''
         Package providing the `ncmpcpp` command.
       '';
       example =
@@ -75,7 +74,7 @@ in {
         else
           null
       '';
-      description = lib.mdDoc ''
+      description = ''
         Value of the `mpd_music_dir` setting. On Linux platforms the
         value of {var}`services.mpd.musicDirectory` is used as the
         default if {var}`services.mpd.enable` is
@@ -87,7 +86,7 @@ in {
     settings = mkOption {
       type = types.attrsOf valueType;
       default = { };
-      description = lib.mdDoc ''
+      description = ''
         Attribute set from name of a setting to its value. For available options
         see
         {manpage}`ncmpcpp(1)`.
@@ -98,7 +97,7 @@ in {
     bindings = mkOption {
       type = types.listOf bindingType;
       default = [ ];
-      description = lib.mdDoc "List of keybindings.";
+      description = "List of keybindings.";
       example = literalExpression ''
         [
           { key = "j"; command = "scroll_down"; }