lib: deprecate unused nmd lib extension

lib/nmd.nix

@@ -1,17 +0,0 @@
-# Copied from nmd master: https://gitlab.com/rycee/nmd/-/blob/master/default.nix?ref_type=heads
-# Allows asciiDoc in options. It is easier to copy & keep updated then figure out how to pass the nmd input
-# along to user modules
-{
-  # Indicates that the given text should be interpreted as AsciiDoc markup.
-  asciiDoc = text: {
-    _type = "asciiDoc";
-    inherit text;
-  };
-
-  # Indicates that the given text should be interpreted as AsciiDoc markup and
-  # used in a literal context.
-  literalAsciiDoc = text: {
-    _type = "literalAsciiDoc";
-    inherit text;
-  };
-}