fix: remove empty custom_dir from mkdocs.yml

The custom_dir: overrides was pointing to an empty directory,
causing zensical build to fail with 'No such file or directory' error.
Remove it since no template overrides are needed.

Author: davidberenstein1957

mkdocs.yml

@@ -95,7 +95,6 @@ extra_css:
 extra_javascript:
   - javascripts/mathjax.js
   - https://unpkg.com/mathjax@3/es5/tex-mml-chtml.js
-  - javascripts/discord-link.js
 
 markdown_extensions:
   - abbr