Replace "rm" call with "git rm"

`git rm` should always be preferred over "normal" `rm`.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

doc/contributing/submitting-changes.chapter.md

@@ -96,7 +96,7 @@ We use jbidwatcher as an example for a discontinued project here.
 
 1. Have Nixpkgs checked out locally and up to date.
 1. Create a new branch for your change, e.g. `git checkout -b jbidwatcher`
-1. Remove the actual package including its directory, e.g. `rm -rf pkgs/applications/misc/jbidwatcher`
+1. Remove the actual package including its directory, e.g. `git rm -rf pkgs/applications/misc/jbidwatcher`
 1. Remove the package from the list of all packages (`pkgs/top-level/all-packages.nix`).
 1. Add an alias for the package name in `pkgs/top-level/aliases.nix` (There is also `pkgs/applications/editors/vim/plugins/aliases.nix`. Package sets typically do not have aliases, so we can't add them there.)