emacs27: Don't pass imagemagick from all-packages
emacs27: Don't pass imagemagick from all-packages

It's already disabled by default in the Emacs expression and passing
`imagemagick = null` makes passing `withImageMagick = true` useless.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs