🌐 Fix incorrect `pymdown-extensions` option used in CJK characters documentation

[andychucs]

The smart_enable option makes the docs not supported to be displayed when using bold and italics which are in Chinese, Japanese, and Korean.

We basically don’t use whitespace between words in Chinese and Japanese.

It causes a lot of problems with Markdown convert. So it should not be set as all just keep default is correct for now.

Check the difference here with search '**' in web documents.

Chinese:

after: https://42bebad1.fastapitiangolo.pages.dev/zh/#sponsors

before: https://fastapi.tiangolo.com/zh/#sponsors

Japanese:

after: https://42bebad1.fastapitiangolo.pages.dev/ja/#sponsors

before: https://fastapi.tiangolo.com/ja/#sponsors

Korean case like this one: https://github.com/fastapi/fastapi/pull/12142