nixos: remove mdDoc from nixos/modules

[philiptaron]

Description of changes

Since #237557 was merged, lib.mdDoc has been a no-op. Let's remove it.

The tracking issue is #300735.

Things done

• nix-build doc/default.nix

[philiptaron]

I can split these up into multiple PRs. Considering how fast a merge conflict came up, I likely should do that.

[emilylange]

Did you do that with just sed?
Because you have trunks that

• drop newlines in inherit (lib) that should stay

• add a comma between the most right key of inherits and the semicolon (;)

• change e.g.

   enable = mkEnableOption (
     lib.mdDoc ''
       lorem ipsum
     ''
   );

  into

   enable = mkEnableOption ( ''
       lorem ipsum
     ''
   );

• replace mkEnableOption (mdDoc "lorem ipsum"); with mkEnableOption ( "lorem ipsum");

• and likely other formatting related issues

How about deferring this until nixfmt (RFC 166) has been run tree-wide?
Or how about a more sophisticated script, if you believe this is worth the effort?

[philiptaron]

I did it a little more sophisticated than sed, with vim and :argdo. I can see that that mkEnableOption commit didn't do it right. I'll pursue both a more targeted approach than 1695 files changed and with a more tested script.