Remove unused custom_templates option from mkdocstrings

We don't use the option and the new version of `mkdocstrings` raises an
error if the directory doesn't exist.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

mkdocs.yml

@@ -100,7 +100,6 @@ plugins:
       alias_type: redirect
       canonical_version: latest
   - mkdocstrings:
-      custom_templates: templates
       default_handler: python
       handlers:
         python: