docs.rs fallout tracking issue

[apoelstra]

This issue is to discuss the follout of the removal of doc_auto_cfg in rust-lang/rust#138907

This has broken our CI across the board because we run a command resembling

export RUSTFLAGS="--cfg docsrs"
export RUSTDOCFLAGS="--cfg docsrs -D warnings -D rustdoc::broken-intra-doc-links" 
cargo +nightly doc --all-features

which attempts to build the crate and all its dependencies with docsrs on, which then enables doc_auto_cfg, which the compiler rejects. However docs.rs doesn't even do this, based on my read of https://github.com/dtolnay/cargo-docs-rs/blob/master/src/main.rs. It only sets docsrs in RUSTDOCFLAGS, not in RUSTFLAGS.

I therefore propose:

• we remove the RUSTFLAGS setting
• we add --no-deps to our cargo doc invocation, so it won't attempt to document dependencies (this also triggers the doc_auto_cfg bug)

in both our CI here and in our local CI.

[apoelstra]

Looks like we have fixed the first thing in #26 99ea567