treewide: remove invalid docbook XML from option descriptions

NixOS will soon use CommonMark Markdown for option descriptions.
We can then switch back the old, slightly clearer bracket syntax.

modules/bitcoind.nix

@@ -120,7 +120,7 @@ let
                 example = "f7efda5c189b999524f151318c0c86$d5b51b3beffbc02b724e5d095828e0bc8b2456e9ac8757ae3211a5d9b16a22ae";
                 description = ''
                   Password HMAC-SHA-256 for JSON-RPC connections. Must be a string of the
-                  format <SALT-HEX>$<HMAC-HEX>.
+                  format `salt-hex$hmac-hex`.
                 '';
               };
               passwordHMACFromFile = mkOption {

modules/liquid.nix

@@ -224,7 +224,7 @@ let
         example = "f7efda5c189b999524f151318c0c86$d5b51b3beffbc02b724e5d095828e0bc8b2456e9ac8757ae3211a5d9b16a22ae";
         description = ''
           Password HMAC-SHA-256 for JSON-RPC connections. Must be a string of the
-          format <SALT-HEX>$<HMAC-HEX>.
+          format `salt-hex$hmac-hex`.
         '';
       };
     };

modules/onion-addresses.nix

@@ -28,7 +28,7 @@ let
       default = [];
       description = ''
         Services that can access their onion address via file
-        /var/lib/onion-addresses/<service>
+        `/var/lib/onion-addresses/$service`
         The file is readable only by the service user.
       '';
     };