chore: Remove doc(html_root_url) attribute from all crates. (tokio-…

…rs#2384)

Fixes tokio-rs#2383.
; Conflicts:
;	tracing-appender/src/lib.rs
;	tracing-attributes/src/lib.rs
;	tracing-core/src/lib.rs
;	tracing-error/src/lib.rs
;	tracing-futures/src/lib.rs
;	tracing-log/src/lib.rs
;	tracing-opentelemetry/src/lib.rs
;	tracing-serde/src/lib.rs
;	tracing-subscriber/src/lib.rs
;	tracing/src/lib.rs

tracing-opentelemetry/src/lib.rs

@@ -100,7 +100,6 @@
 //! [subscriber]: tracing_subscriber::subscribe
 #![deny(unreachable_pub)]
 #![cfg_attr(test, deny(warnings))]
-#![doc(html_root_url = "https://docs.rs/tracing-opentelemetry/0.18.0")]
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png",
     issue_tracker_base_url = "https://github.com/tokio-rs/tracing/issues/"