Don't set html_root_url

The recommendation to set this has been removed from the Rust API
guidelines:

rust-lang/api-guidelines#230

It used to be used by docs.rs, but docs.rs now unconditionally sets the
`--extern-html-root-url` parameter of rustdoc which overrides it, making
it no longer needed and superfluous.

Author: tarcieri

Cargo.toml

@@ -2,7 +2,6 @@
 name = "curve25519-dalek"
 # Before incrementing:
 # - update CHANGELOG
-# - update html_root_url
 # - update README if required by semver
 # - if README was updated, also update module documentation in src/lib.rs
 version = "4.0.0-pre.5"

src/lib.rs

@@ -20,7 +20,6 @@
 #![doc(
     html_logo_url = "https://cdn.jsdelivr.net/gh/dalek-cryptography/curve25519-dalek/docs/assets/dalek-logo-clear.png"
 )]
-#![doc(html_root_url = "https://docs.rs/curve25519-dalek/4.0.0-pre.5")]
 #![doc = include_str!("../README.md")]
 
 //------------------------------------------------------------------------