`CONTRIBUTING.md` instructions for `rust-analyzer` are outdated

[nsunderland1]

Description

The rust-analyzer section in CONTRIBUTING.md suggests setting "rust-analyzer.updates.channel": "nightly". This setting was recently removed from rust-analyzer. Not sure whether the setting is no longer necessary to get type hints to work in Clippy, or if there's an alternative method that needs to be added to the docs here.

Version

rustc 1.60.0-nightly (e7aca8959 2022-02-09)
binary: rustc
commit-hash: e7aca895980f25f6d2d3c48e10fd04656764d1e4
commit-date: 2022-02-09
host: x86_64-unknown-linux-gnu
release: 1.60.0-nightly
LLVM version: 13.0.0

Additional Labels

@rustbot label +A-documentation