The notion extends to official libraries, not just the language itself. That said, I'm not the best person to ask, but cursory research turns up a few examples.[0][1][2][3]
Some of these aren't examples of legacy cruft per se. However, as complexity is added to a language at a rapid rate, there becomes more confusion over what best practice actually is.
[0] https://www.reddit.com/r/rust/comments/2r7ttq/where_to_find_...
[1] https://users.rust-lang.org/t/rust-version-support-in-librar...
[2] https://gist.github.com/lifthrasiir/cedb5db8dbcd209c5957
[3] https://users.rust-lang.org/t/is-this-idiomatic-rust/2155
What is considered legacy cruft in Rust? The only change I'm aware of was the introduction of the `?` operator to replace the `try!` macro. That's easy to find/replace.