Switch rustdoc logging to RUSTDOC_LOG
Switch rustdoc logging to RUSTDOC_LOG

This better aligns with Cargo (CARGO_LOG) and rustc (RUSTC_LOG).

graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust