Unset mn5 default bash functions in nix-portable

Reviewed-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

pkgs/nix-portable/default.nix

@@ -268,6 +268,9 @@ let
     export SHELL="${pkgs.bashInteractive.out}/bin/bash"
     export PS1="\n\[\033[1;32m\][\[\e]0;\u@\h: \w\a\]\u@\h:\w]\$\[\033[0m\] "
 
+    # unset bash function aliases
+    unset -f which ml module
+
     ### setup SSL
     # find ssl certs or use from nixpkgs
     debug "figuring out ssl certs"