configuration.nix: don't use obsidian.nvim

Obsidian essentially requires direct configuration, is not for a generic config example config.
It isn't enabled now, so removing it should be fine.

Author: alfarelcynthesis

configuration.nix

@@ -214,7 +214,6 @@ isMaximal: {
     };
 
     notes = {
-      obsidian.enable = false; # FIXME: neovim fails to build if obsidian is enabled
       neorg.enable = false;
       orgmode.enable = false;
       mind-nvim.enable = isMaximal;