gnu: Remove rust-tempfile-3.0.

* gnu/packages/crates-io.scm (rust-tempfile-3.0): Remove variable.
(rust-compiletest-rs-0.3, rust-filetime-0.2, rust-handlebars-2.0,
rust-nix-0.15, rust-nix-0.14, rust-proptest-0.9, rust-proptest-0.8,
rust-rustls-0.16, rust-rusty-fork-0.2, rust-tiff-0.2, rust-tokei-fs-0.1,
rust-tokio-uds-0.2, rust-xattr-0.2) [arguments]: Replace
rust-tempfile-3.0 with 3.1.
* gnu/packages/rust-apps.scm (tokei)[arguments]: Same.