remove text-direction from book.toml

[szabgab]

setting the language to "fa" should make the book rtl

As far as I know text-direction = "rtl" is now unnecessary as the language = "fa" setting should already sets the book to rtl. https://github.com/rust-lang/mdBook/blob/3052fe38270bb370dcf54009d450c5395537d975/src/config.rs#L466

Currently this is the only mdboik I am aware of that uses this option. See https://mdbooks.code-maven.com/text-direction

Before I propose the change to the mdbook project, I'd like to ask you to verify that indeed the language = "fa" setting is enough for you as well.

[drunkleen]

You're absolutely right, setting language = "fa" in book.toml does indeed render the book in RTL format without needing the explicit text-direction = "rtl" setting.
I appreciate you bringing this to my attention. I added that line because I had some experience with older versions of mdBook and faced issues with text align in Persian and based on that, I added that setting.