Remove support for hosting under sub dir

[SuperKenVery]

dioxus barely supports this.

• It doesn't support runtime configuration of sub path, which is required if we want to read from config file.
• It panics if I set one in Dioxus.toml. Even before panic, there are many strange cookie-refresh logs in server. Clearly this isn't tested very much, I'm afraid there would be more pitfalls.