Motivation for this change

I want to use bottom on my raspberry pi, but it didn't build.

Things done

Remove a cargo config included in the bottom repository, because it sets the aarch64 compiler to something that doesn't exist in our environment. I didn't see anything useful in this file, since it would all be handled by the nixpkgs Rust infrastructure for different platforms and cross-compilation cases.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.