Cleanup weird default runner binaries

[Nemo157]

Run hecrj/setup-rust-action@v1
/home/runner/.cargo/bin/rustup self update
info: checking for self-updates
  rustup unchanged - 1.25.1

warning: tool `rustfmt` is already installed, remove it from `/home/runner/.cargo/bin`, then run `rustup update` to have rustup manage this tool.
warning: tool `cargo-fmt` is already installed, remove it from `/home/runner/.cargo/bin`, then run `rustup update` to have rustup manage this tool.

For some reason the default linux and windows runners have some rustfmt and cargo-fmt binaries that aren't hard-links to rustup. They do appear to be rustup instances since they obey the rustup default setting, but the rustup self update won't update them and potentially cause issues from inconsistent versions of rustup being used.

These could just be deleted before running rustup self update and then rustup will correctly restore them as hard-links to itself.