`:reload` in the REPL removes everything loaded with `:lf`

[thufschmitt]

If a flake is loaded with :lf in the repl, then running :r will drop it from the environment rather than reloading it:

$ nix repl
Welcome to Nix 2.17.0pre20230720_85d0eb6. Type :? for help.

nix-repl> :lf nixpkgs    
Added 15 variables.

nix-repl> builtins.attrNames legacyPackages 
[ "aarch64-darwin" "aarch64-linux" "armv5tel-linux" "armv6l-linux" "armv7l-linux" "i686-linux" "mipsel-linux" "powerpc64le-linux" "riscv64-linux" "x86_64-darwin" "x86_64-linux" ]

nix-repl> :r                                

nix-repl> builtins.attrNames legacyPackages
error: undefined variable 'legacyPackages'

       at «string»:1:20:

            1| builtins.attrNames legacyPackages
             |                    ^

This doesn't affect :l